This patch creates a generic process container system based on (and parallel top) the cpusets code. At a coarse level it was created by copying kernel/cpuset.c, doing s/cpuset/container/g, and stripping out any code that was cpuset-specific rather than applicable to any process container subsystem. Signed-off-by: Paul Menage --- Documentation/containers.txt | 229 +++++++ fs/proc/base.c | 11 include/linux/container.h | 96 +++ include/linux/sched.h | 5 init/Kconfig | 9 init/main.c | 3 kernel/Makefile | 1 kernel/container.c | 1343 +++++++++++++++++++++++++++++++++++++++++++ kernel/exit.c | 2 kernel/fork.c | 3 10 files changed, 1699 insertions(+), 3 deletions(-) Index: container-2.6.19-rc5/fs/proc/base.c =================================================================== --- container-2.6.19-rc5.orig/fs/proc/base.c +++ container-2.6.19-rc5/fs/proc/base.c @@ -68,6 +68,7 @@ #include #include #include +#include #include #include #include @@ -1782,7 +1783,10 @@ static struct pid_entry tgid_base_stuff[ #ifdef CONFIG_SCHEDSTATS INF("schedstat", S_IRUGO, pid_schedstat), #endif -#ifdef CONFIG_CPUSETS +#ifdef CONFIG_CONTAINERS + REG("container", S_IRUGO, container), +#endif +#ifdef CONFIG_PROC_PID_CPUSET REG("cpuset", S_IRUGO, cpuset), #endif INF("oom_score", S_IRUGO, oom_score), @@ -2056,7 +2060,10 @@ static struct pid_entry tid_base_stuff[] #ifdef CONFIG_SCHEDSTATS INF("schedstat", S_IRUGO, pid_schedstat), #endif -#ifdef CONFIG_CPUSETS +#ifdef CONFIG_CONTAINERS + REG("container", S_IRUGO, container), +#endif +#ifdef CONFIG_PROC_PID_CPUSET REG("cpuset", S_IRUGO, cpuset), #endif INF("oom_score", S_IRUGO, oom_score), Index: container-2.6.19-rc5/include/linux/container.h =================================================================== --- /dev/null +++ container-2.6.19-rc5/include/linux/container.h @@ -0,0 +1,96 @@ +#ifndef _LINUX_CONTAINER_H +#define _LINUX_CONTAINER_H +/* + * container interface + * + * Copyright (C) 2003 BULL SA + * Copyright (C) 2004-2006 Silicon Graphics, Inc. + * + */ + +#include +#include +#include + +#ifdef CONFIG_CONTAINERS + +extern int number_of_containers; /* How many containers are defined in system? */ + +extern int container_init_early(void); +extern int container_init(void); +extern void container_init_smp(void); +extern void container_fork(struct task_struct *p); +extern void container_exit(struct task_struct *p); + +extern struct file_operations proc_container_operations; + +extern void container_lock(void); +extern void container_unlock(void); + +extern void container_manage_lock(void); +extern void container_manage_unlock(void); + +struct container { + unsigned long flags; /* "unsigned long" so bitops work */ + + /* + * Count is atomic so can incr (fork) or decr (exit) without a lock. + */ + atomic_t count; /* count tasks using this container */ + + /* + * We link our 'sibling' struct into our parent's 'children'. + * Our children link their 'sibling' into our 'children'. + */ + struct list_head sibling; /* my parent's children */ + struct list_head children; /* my children */ + + struct container *parent; /* my parent */ + struct dentry *dentry; /* container fs entry */ +}; + +/* struct cftype: + * + * The files in the container filesystem mostly have a very simple read/write + * handling, some common function will take care of it. Nevertheless some cases + * (read tasks) are special and therefore I define this structure for every + * kind of file. + * + * + * When reading/writing to a file: + * - the container to use in file->f_dentry->d_parent->d_fsdata + * - the 'cftype' of the file is file->f_dentry->d_fsdata + */ + +struct inode; +struct cftype { + char *name; + int private; + int (*open) (struct inode *inode, struct file *file); + ssize_t (*read) (struct container *cont, struct cftype *cft, + struct file *file, + char __user *buf, size_t nbytes, loff_t *ppos); + ssize_t (*write) (struct container *cont, struct cftype *cft, + struct file *file, + const char __user *buf, size_t nbytes, loff_t *ppos); + int (*release) (struct inode *inode, struct file *file); +}; + +int container_add_file(struct container *cont, const struct cftype *cft); + +int container_is_removed(const struct container *cont); + +#else /* !CONFIG_CONTAINERS */ + +static inline int container_init_early(void) { return 0; } +static inline int container_init(void) { return 0; } +static inline void container_init_smp(void) {} +static inline void container_fork(struct task_struct *p) {} +static inline void container_exit(struct task_struct *p) {} + +static inline void container_lock(void) {} +static inline void container_unlock(void) {} + +#endif /* !CONFIG_CONTAINERS */ + +#endif /* _LINUX_CONTAINER_H */ Index: container-2.6.19-rc5/include/linux/sched.h =================================================================== --- container-2.6.19-rc5.orig/include/linux/sched.h +++ container-2.6.19-rc5/include/linux/sched.h @@ -719,8 +719,8 @@ extern unsigned int max_cache_size; struct io_context; /* See blkdev.h */ +struct container; struct cpuset; - #define NGROUPS_SMALL 32 #define NGROUPS_PER_BLOCK ((int)(PAGE_SIZE / sizeof(gid_t))) struct group_info { @@ -1006,6 +1006,9 @@ struct task_struct { int cpuset_mems_generation; int cpuset_mem_spread_rotor; #endif +#ifdef CONFIG_CONTAINERS + struct container *container; +#endif struct robust_list_head __user *robust_list; #ifdef CONFIG_COMPAT struct compat_robust_list_head __user *compat_robust_list; Index: container-2.6.19-rc5/init/Kconfig =================================================================== --- container-2.6.19-rc5.orig/init/Kconfig +++ container-2.6.19-rc5/init/Kconfig @@ -238,6 +238,15 @@ config IKCONFIG_PROC This option enables access to the kernel configuration file through /proc/config.gz. +config CONTAINERS + bool "Container support" + help + This option will let you create and manage process containers, + which can be used to aggregate multiple processes, e.g. for + the purposes of resource tracking. + + Say N if unsure + config CPUSETS bool "Cpuset support" depends on SMP Index: container-2.6.19-rc5/init/main.c =================================================================== --- container-2.6.19-rc5.orig/init/main.c +++ container-2.6.19-rc5/init/main.c @@ -38,6 +38,7 @@ #include #include #include +#include #include #include #include @@ -568,6 +569,7 @@ asmlinkage void __init start_kernel(void } #endif vfs_caches_init_early(); + container_init_early(); cpuset_init_early(); mem_init(); kmem_cache_init(); @@ -598,6 +600,7 @@ asmlinkage void __init start_kernel(void #ifdef CONFIG_PROC_FS proc_root_init(); #endif + container_init(); cpuset_init(); taskstats_init_early(); delayacct_init(); Index: container-2.6.19-rc5/kernel/container.c =================================================================== --- /dev/null +++ container-2.6.19-rc5/kernel/container.c @@ -0,0 +1,1343 @@ +/* + * kernel/container.c + * + * Generic process-grouping system. + * + * Based originally on the cpuset system, extracted by Paul Menage + * Copyright (C) 2006 Google, Inc + * + * Copyright notices from the original cpuset code: + * -------------------------------------------------- + * Copyright (C) 2003 BULL SA. + * Copyright (C) 2004-2006 Silicon Graphics, Inc. + * + * Portions derived from Patrick Mochel's sysfs code. + * sysfs is Copyright (c) 2001-3 Patrick Mochel + * + * 2003-10-10 Written by Simon Derr. + * 2003-10-22 Updates by Stephen Hemminger. + * 2004 May-July Rework by Paul Jackson. + * --------------------------------------------------- + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of the Linux + * distribution for more details. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include + +#define CONTAINER_SUPER_MAGIC 0x27e0eb + +/* + * Tracks how many containers are currently defined in system. + * When there is only one container (the root container) we can + * short circuit some hooks. + */ +int number_of_containers __read_mostly; + +/* bits in struct container flags field */ +typedef enum { + CONT_REMOVED, + CONT_NOTIFY_ON_RELEASE, +} container_flagbits_t; + +/* convenient tests for these bits */ +inline int container_is_removed(const struct container *cont) +{ + return test_bit(CONT_REMOVED, &cont->flags); +} + +static inline int notify_on_release(const struct container *cont) +{ + return test_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags); +} + +static struct container top_container = { + .count = ATOMIC_INIT(0), + .sibling = LIST_HEAD_INIT(top_container.sibling), + .children = LIST_HEAD_INIT(top_container.children), +}; + +static struct vfsmount *container_mount; +static struct super_block *container_sb; + +/* + * We have two global container mutexes below. They can nest. + * It is ok to first take manage_mutex, then nest callback_mutex. We also + * require taking task_lock() when dereferencing a tasks container pointer. + * See "The task_lock() exception", at the end of this comment. + * + * A task must hold both mutexes to modify containers. If a task + * holds manage_mutex, then it blocks others wanting that mutex, + * ensuring that it is the only task able to also acquire callback_mutex + * and be able to modify containers. It can perform various checks on + * the container structure first, knowing nothing will change. It can + * also allocate memory while just holding manage_mutex. While it is + * performing these checks, various callback routines can briefly + * acquire callback_mutex to query containers. Once it is ready to make + * the changes, it takes callback_mutex, blocking everyone else. + * + * Calls to the kernel memory allocator can not be made while holding + * callback_mutex, as that would risk double tripping on callback_mutex + * from one of the callbacks into the container code from within + * __alloc_pages(). + * + * If a task is only holding callback_mutex, then it has read-only + * access to containers. + * + * The task_struct fields mems_allowed and mems_generation may only + * be accessed in the context of that task, so require no locks. + * + * Any task can increment and decrement the count field without lock. + * So in general, code holding manage_mutex or callback_mutex can't rely + * on the count field not changing. However, if the count goes to + * zero, then only attach_task(), which holds both mutexes, can + * increment it again. Because a count of zero means that no tasks + * are currently attached, therefore there is no way a task attached + * to that container can fork (the other way to increment the count). + * So code holding manage_mutex or callback_mutex can safely assume that + * if the count is zero, it will stay zero. Similarly, if a task + * holds manage_mutex or callback_mutex on a container with zero count, it + * knows that the container won't be removed, as container_rmdir() needs + * both of those mutexes. + * + * The container_common_file_write handler for operations that modify + * the container hierarchy holds manage_mutex across the entire operation, + * single threading all such container modifications across the system. + * + * The container_common_file_read() handlers only hold callback_mutex across + * small pieces of code, such as when reading out possibly multi-word + * cpumasks and nodemasks. + * + * The fork and exit callbacks container_fork() and container_exit(), don't + * (usually) take either mutex. These are the two most performance + * critical pieces of code here. The exception occurs on container_exit(), + * when a task in a notify_on_release container exits. Then manage_mutex + * is taken, and if the container count is zero, a usermode call made + * to /sbin/container_release_agent with the name of the container (path + * relative to the root of container file system) as the argument. + * + * A container can only be deleted if both its 'count' of using tasks + * is zero, and its list of 'children' containers is empty. Since all + * tasks in the system use _some_ container, and since there is always at + * least one task in the system (init, pid == 1), therefore, top_container + * always has either children containers and/or using tasks. So we don't + * need a special hack to ensure that top_container cannot be deleted. + * + * The above "Tale of Two Semaphores" would be complete, but for: + * + * The task_lock() exception + * + * The need for this exception arises from the action of attach_task(), + * which overwrites one tasks container pointer with another. It does + * so using both mutexes, however there are several performance + * critical places that need to reference task->container without the + * expense of grabbing a system global mutex. Therefore except as + * noted below, when dereferencing or, as in attach_task(), modifying + * a tasks container pointer we use task_lock(), which acts on a spinlock + * (task->alloc_lock) already in the task_struct routinely used for + * such matters. + * + * P.S. One more locking exception. RCU is used to guard the + * update of a tasks container pointer by attach_task() and the + * access of task->container->mems_generation via that pointer in + * the routine container_update_task_memory_state(). + */ + +static DEFINE_MUTEX(manage_mutex); +static DEFINE_MUTEX(callback_mutex); + +/* + * A couple of forward declarations required, due to cyclic reference loop: + * container_mkdir -> container_create -> container_populate_dir -> container_add_file + * -> container_create_file -> container_dir_inode_operations -> container_mkdir. + */ + +static int container_mkdir(struct inode *dir, struct dentry *dentry, int mode); +static int container_rmdir(struct inode *unused_dir, struct dentry *dentry); + +static struct backing_dev_info container_backing_dev_info = { + .ra_pages = 0, /* No readahead */ + .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK, +}; + +static struct inode *container_new_inode(mode_t mode) +{ + struct inode *inode = new_inode(container_sb); + + if (inode) { + inode->i_mode = mode; + inode->i_uid = current->fsuid; + inode->i_gid = current->fsgid; + inode->i_blocks = 0; + inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; + inode->i_mapping->backing_dev_info = &container_backing_dev_info; + } + return inode; +} + +static void container_diput(struct dentry *dentry, struct inode *inode) +{ + /* is dentry a directory ? if so, kfree() associated container */ + if (S_ISDIR(inode->i_mode)) { + struct container *cont = dentry->d_fsdata; + BUG_ON(!(container_is_removed(cont))); + kfree(cont); + } + iput(inode); +} + +static struct dentry_operations container_dops = { + .d_iput = container_diput, +}; + +static struct dentry *container_get_dentry(struct dentry *parent, const char *name) +{ + struct dentry *d = lookup_one_len(name, parent, strlen(name)); + if (!IS_ERR(d)) + d->d_op = &container_dops; + return d; +} + +static void remove_dir(struct dentry *d) +{ + struct dentry *parent = dget(d->d_parent); + + d_delete(d); + simple_rmdir(parent->d_inode, d); + dput(parent); +} + +/* + * NOTE : the dentry must have been dget()'ed + */ +static void container_d_remove_dir(struct dentry *dentry) +{ + struct list_head *node; + + spin_lock(&dcache_lock); + node = dentry->d_subdirs.next; + while (node != &dentry->d_subdirs) { + struct dentry *d = list_entry(node, struct dentry, d_u.d_child); + list_del_init(node); + if (d->d_inode) { + d = dget_locked(d); + spin_unlock(&dcache_lock); + d_delete(d); + simple_unlink(dentry->d_inode, d); + dput(d); + spin_lock(&dcache_lock); + } + node = dentry->d_subdirs.next; + } + list_del_init(&dentry->d_u.d_child); + spin_unlock(&dcache_lock); + remove_dir(dentry); +} + +static struct super_operations container_ops = { + .statfs = simple_statfs, + .drop_inode = generic_delete_inode, +}; + +static int container_fill_super(struct super_block *sb, void *unused_data, + int unused_silent) +{ + struct inode *inode; + struct dentry *root; + + sb->s_blocksize = PAGE_CACHE_SIZE; + sb->s_blocksize_bits = PAGE_CACHE_SHIFT; + sb->s_magic = CONTAINER_SUPER_MAGIC; + sb->s_op = &container_ops; + container_sb = sb; + + inode = container_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR); + if (inode) { + inode->i_op = &simple_dir_inode_operations; + inode->i_fop = &simple_dir_operations; + /* directories start off with i_nlink == 2 (for "." entry) */ + inode->i_nlink++; + } else { + return -ENOMEM; + } + + root = d_alloc_root(inode); + if (!root) { + iput(inode); + return -ENOMEM; + } + sb->s_root = root; + return 0; +} + +static int container_get_sb(struct file_system_type *fs_type, + int flags, const char *unused_dev_name, + void *data, struct vfsmount *mnt) +{ + return get_sb_single(fs_type, flags, data, container_fill_super, mnt); +} + +static struct file_system_type container_fs_type = { + .name = "container", + .get_sb = container_get_sb, + .kill_sb = kill_litter_super, +}; + +static inline struct container *__d_cont(struct dentry *dentry) +{ + return dentry->d_fsdata; +} + +static inline struct cftype *__d_cft(struct dentry *dentry) +{ + return dentry->d_fsdata; +} + +/* + * Call with manage_mutex held. Writes path of container into buf. + * Returns 0 on success, -errno on error. + */ + +static int container_path(const struct container *cont, char *buf, int buflen) +{ + char *start; + + start = buf + buflen; + + *--start = '\0'; + for (;;) { + int len = cont->dentry->d_name.len; + if ((start -= len) < buf) + return -ENAMETOOLONG; + memcpy(start, cont->dentry->d_name.name, len); + cont = cont->parent; + if (!cont) + break; + if (!cont->parent) + continue; + if (--start < buf) + return -ENAMETOOLONG; + *start = '/'; + } + memmove(buf, start, buf + buflen - start); + return 0; +} + +/* + * Notify userspace when a container is released, by running + * /sbin/container_release_agent with the name of the container (path + * relative to the root of container file system) as the argument. + * + * Most likely, this user command will try to rmdir this container. + * + * This races with the possibility that some other task will be + * attached to this container before it is removed, or that some other + * user task will 'mkdir' a child container of this container. That's ok. + * The presumed 'rmdir' will fail quietly if this container is no longer + * unused, and this container will be reprieved from its death sentence, + * to continue to serve a useful existence. Next time it's released, + * we will get notified again, if it still has 'notify_on_release' set. + * + * The final arg to call_usermodehelper() is 0, which means don't + * wait. The separate /sbin/container_release_agent task is forked by + * call_usermodehelper(), then control in this thread returns here, + * without waiting for the release agent task. We don't bother to + * wait because the caller of this routine has no use for the exit + * status of the /sbin/container_release_agent task, so no sense holding + * our caller up for that. + * + * When we had only one container mutex, we had to call this + * without holding it, to avoid deadlock when call_usermodehelper() + * allocated memory. With two locks, we could now call this while + * holding manage_mutex, but we still don't, so as to minimize + * the time manage_mutex is held. + */ + +static void container_release_agent(const char *pathbuf) +{ + char *argv[3], *envp[3]; + int i; + + if (!pathbuf) + return; + + i = 0; + argv[i++] = "/sbin/container_release_agent"; + argv[i++] = (char *)pathbuf; + argv[i] = NULL; + + i = 0; + /* minimal command environment */ + envp[i++] = "HOME=/"; + envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin"; + envp[i] = NULL; + + call_usermodehelper(argv[0], argv, envp, 0); + kfree(pathbuf); +} + +/* + * Either cont->count of using tasks transitioned to zero, or the + * cont->children list of child containers just became empty. If this + * cont is notify_on_release() and now both the user count is zero and + * the list of children is empty, prepare container path in a kmalloc'd + * buffer, to be returned via ppathbuf, so that the caller can invoke + * container_release_agent() with it later on, once manage_mutex is dropped. + * Call here with manage_mutex held. + * + * This check_for_release() routine is responsible for kmalloc'ing + * pathbuf. The above container_release_agent() is responsible for + * kfree'ing pathbuf. The caller of these routines is responsible + * for providing a pathbuf pointer, initialized to NULL, then + * calling check_for_release() with manage_mutex held and the address + * of the pathbuf pointer, then dropping manage_mutex, then calling + * container_release_agent() with pathbuf, as set by check_for_release(). + */ + +static void check_for_release(struct container *cont, char **ppathbuf) +{ + if (notify_on_release(cont) && atomic_read(&cont->count) == 0 && + list_empty(&cont->children)) { + char *buf; + + buf = kmalloc(PAGE_SIZE, GFP_KERNEL); + if (!buf) + return; + if (container_path(cont, buf, PAGE_SIZE) < 0) + kfree(buf); + else + *ppathbuf = buf; + } +} + + +/* + * update_flag - read a 0 or a 1 in a file and update associated flag + * bit: the bit to update (CONT_NOTIFY_ON_RELEASE) + * cont: the container to update + * buf: the buffer where we read the 0 or 1 + * + * Call with manage_mutex held. + */ + +static int update_flag(container_flagbits_t bit, struct container *cont, char *buf) +{ + int turning_on; + + turning_on = (simple_strtoul(buf, NULL, 10) != 0); + + mutex_lock(&callback_mutex); + if (turning_on) + set_bit(bit, &cont->flags); + else + clear_bit(bit, &cont->flags); + mutex_unlock(&callback_mutex); + + return 0; +} + + +/* + * Attack task specified by pid in 'pidbuf' to container 'cont', possibly + * writing the path of the old container in 'ppathbuf' if it needs to be + * notified on release. + * + * Call holding manage_mutex. May take callback_mutex and task_lock of + * the task 'pid' during call. + */ + +static int attach_task(struct container *cont, char *pidbuf, char **ppathbuf) +{ + pid_t pid; + struct task_struct *tsk; + struct container *oldcont; + int retval; + + if (sscanf(pidbuf, "%d", &pid) != 1) + return -EIO; + + if (pid) { + read_lock(&tasklist_lock); + + tsk = find_task_by_pid(pid); + if (!tsk || tsk->flags & PF_EXITING) { + read_unlock(&tasklist_lock); + return -ESRCH; + } + + get_task_struct(tsk); + read_unlock(&tasklist_lock); + + if ((current->euid) && (current->euid != tsk->uid) + && (current->euid != tsk->suid)) { + put_task_struct(tsk); + return -EACCES; + } + } else { + tsk = current; + get_task_struct(tsk); + } + + retval = security_task_setscheduler(tsk, 0, NULL); + if (retval) { + put_task_struct(tsk); + return retval; + } + + mutex_lock(&callback_mutex); + + task_lock(tsk); + oldcont = tsk->container; + if (!oldcont) { + task_unlock(tsk); + mutex_unlock(&callback_mutex); + put_task_struct(tsk); + return -ESRCH; + } + atomic_inc(&cont->count); + rcu_assign_pointer(tsk->container, cont); + task_unlock(tsk); + + mutex_unlock(&callback_mutex); + + put_task_struct(tsk); + synchronize_rcu(); + if (atomic_dec_and_test(&oldcont->count)) + check_for_release(oldcont, ppathbuf); + return 0; +} + +/* The various types of files and directories in a container file system */ + +typedef enum { + FILE_ROOT, + FILE_DIR, + FILE_NOTIFY_ON_RELEASE, + FILE_TASKLIST, +} container_filetype_t; + +static ssize_t container_common_file_write(struct container *cont, + struct cftype *cft, + struct file *file, + const char __user *userbuf, + size_t nbytes, loff_t *unused_ppos) +{ + container_filetype_t type = cft->private; + char *buffer; + char *pathbuf = NULL; + int retval = 0; + + /* Crude upper limit on largest legitimate cpulist user might write. */ + if (nbytes > 100 + 6 * NR_CPUS) + return -E2BIG; + + /* +1 for nul-terminator */ + if ((buffer = kmalloc(nbytes + 1, GFP_KERNEL)) == 0) + return -ENOMEM; + + if (copy_from_user(buffer, userbuf, nbytes)) { + retval = -EFAULT; + goto out1; + } + buffer[nbytes] = 0; /* nul-terminate */ + + mutex_lock(&manage_mutex); + + if (container_is_removed(cont)) { + retval = -ENODEV; + goto out2; + } + + switch (type) { + case FILE_NOTIFY_ON_RELEASE: + retval = update_flag(CONT_NOTIFY_ON_RELEASE, cont, buffer); + break; + case FILE_TASKLIST: + retval = attach_task(cont, buffer, &pathbuf); + break; + default: + retval = -EINVAL; + goto out2; + } + + if (retval == 0) + retval = nbytes; +out2: + mutex_unlock(&manage_mutex); + container_release_agent(pathbuf); +out1: + kfree(buffer); + return retval; +} + +static ssize_t container_file_write(struct file *file, const char __user *buf, + size_t nbytes, loff_t *ppos) +{ + ssize_t retval = 0; + struct cftype *cft = __d_cft(file->f_dentry); + struct container *cont = __d_cont(file->f_dentry->d_parent); + if (!cft) + return -ENODEV; + + /* special function ? */ + if (cft->write) + retval = cft->write(cont, cft, file, buf, nbytes, ppos); + else + retval = -EINVAL; + + return retval; +} + +static ssize_t container_common_file_read(struct container *cont, + struct cftype *cft, + struct file *file, + char __user *buf, + size_t nbytes, loff_t *ppos) +{ + container_filetype_t type = cft->private; + char *page; + ssize_t retval = 0; + char *s; + + if (!(page = (char *)__get_free_page(GFP_KERNEL))) + return -ENOMEM; + + s = page; + + switch (type) { + case FILE_NOTIFY_ON_RELEASE: + *s++ = notify_on_release(cont) ? '1' : '0'; + break; + default: + retval = -EINVAL; + goto out; + } + *s++ = '\n'; + + retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page); +out: + free_page((unsigned long)page); + return retval; +} + +static ssize_t container_file_read(struct file *file, char __user *buf, size_t nbytes, + loff_t *ppos) +{ + ssize_t retval = 0; + struct cftype *cft = __d_cft(file->f_dentry); + struct container *cont = __d_cont(file->f_dentry->d_parent); + if (!cft) + return -ENODEV; + + /* special function ? */ + if (cft->read) + retval = cft->read(cont, cft, file, buf, nbytes, ppos); + else + retval = -EINVAL; + + return retval; +} + +static int container_file_open(struct inode *inode, struct file *file) +{ + int err; + struct cftype *cft; + + err = generic_file_open(inode, file); + if (err) + return err; + + cft = __d_cft(file->f_dentry); + if (!cft) + return -ENODEV; + if (cft->open) + err = cft->open(inode, file); + else + err = 0; + + return err; +} + +static int container_file_release(struct inode *inode, struct file *file) +{ + struct cftype *cft = __d_cft(file->f_dentry); + if (cft->release) + return cft->release(inode, file); + return 0; +} + +/* + * container_rename - Only allow simple rename of directories in place. + */ +static int container_rename(struct inode *old_dir, struct dentry *old_dentry, + struct inode *new_dir, struct dentry *new_dentry) +{ + if (!S_ISDIR(old_dentry->d_inode->i_mode)) + return -ENOTDIR; + if (new_dentry->d_inode) + return -EEXIST; + if (old_dir != new_dir) + return -EIO; + return simple_rename(old_dir, old_dentry, new_dir, new_dentry); +} + +static struct file_operations container_file_operations = { + .read = container_file_read, + .write = container_file_write, + .llseek = generic_file_llseek, + .open = container_file_open, + .release = container_file_release, +}; + +static struct inode_operations container_dir_inode_operations = { + .lookup = simple_lookup, + .mkdir = container_mkdir, + .rmdir = container_rmdir, + .rename = container_rename, +}; + +static int container_create_file(struct dentry *dentry, int mode) +{ + struct inode *inode; + + if (!dentry) + return -ENOENT; + if (dentry->d_inode) + return -EEXIST; + + inode = container_new_inode(mode); + if (!inode) + return -ENOMEM; + + if (S_ISDIR(mode)) { + inode->i_op = &container_dir_inode_operations; + inode->i_fop = &simple_dir_operations; + + /* start off with i_nlink == 2 (for "." entry) */ + inode->i_nlink++; + } else if (S_ISREG(mode)) { + inode->i_size = 0; + inode->i_fop = &container_file_operations; + } + + d_instantiate(dentry, inode); + dget(dentry); /* Extra count - pin the dentry in core */ + return 0; +} + +/* + * container_create_dir - create a directory for an object. + * cont: the container we create the directory for. + * It must have a valid ->parent field + * And we are going to fill its ->dentry field. + * name: The name to give to the container directory. Will be copied. + * mode: mode to set on new directory. + */ + +static int container_create_dir(struct container *cont, const char *name, int mode) +{ + struct dentry *dentry = NULL; + struct dentry *parent; + int error = 0; + + parent = cont->parent->dentry; + dentry = container_get_dentry(parent, name); + if (IS_ERR(dentry)) + return PTR_ERR(dentry); + error = container_create_file(dentry, S_IFDIR | mode); + if (!error) { + dentry->d_fsdata = cont; + parent->d_inode->i_nlink++; + cont->dentry = dentry; + } + dput(dentry); + + return error; +} + +int container_add_file(struct container *cont, const struct cftype *cft) +{ + struct dentry *dir = cont->dentry; + struct dentry *dentry; + int error; + + mutex_lock(&dir->d_inode->i_mutex); + dentry = container_get_dentry(dir, cft->name); + if (!IS_ERR(dentry)) { + error = container_create_file(dentry, 0644 | S_IFREG); + if (!error) + dentry->d_fsdata = (void *)cft; + dput(dentry); + } else + error = PTR_ERR(dentry); + mutex_unlock(&dir->d_inode->i_mutex); + return error; +} + +/* + * Stuff for reading the 'tasks' file. + * + * Reading this file can return large amounts of data if a container has + * *lots* of attached tasks. So it may need several calls to read(), + * but we cannot guarantee that the information we produce is correct + * unless we produce it entirely atomically. + * + * Upon tasks file open(), a struct ctr_struct is allocated, that + * will have a pointer to an array (also allocated here). The struct + * ctr_struct * is stored in file->private_data. Its resources will + * be freed by release() when the file is closed. The array is used + * to sprintf the PIDs and then used by read(). + */ + +/* containers_tasks_read array */ + +struct ctr_struct { + char *buf; + int bufsz; +}; + +/* + * Load into 'pidarray' up to 'npids' of the tasks using container 'cont'. + * Return actual number of pids loaded. No need to task_lock(p) + * when reading out p->container, as we don't really care if it changes + * on the next cycle, and we are not going to try to dereference it. + */ +static int pid_array_load(pid_t *pidarray, int npids, struct container *cont) +{ + int n = 0; + struct task_struct *g, *p; + + read_lock(&tasklist_lock); + + do_each_thread(g, p) { + if (p->container == cont) { + pidarray[n++] = p->pid; + if (unlikely(n == npids)) + goto array_full; + } + } while_each_thread(g, p); + +array_full: + read_unlock(&tasklist_lock); + return n; +} + +static int cmppid(const void *a, const void *b) +{ + return *(pid_t *)a - *(pid_t *)b; +} + +/* + * Convert array 'a' of 'npids' pid_t's to a string of newline separated + * decimal pids in 'buf'. Don't write more than 'sz' chars, but return + * count 'cnt' of how many chars would be written if buf were large enough. + */ +static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids) +{ + int cnt = 0; + int i; + + for (i = 0; i < npids; i++) + cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]); + return cnt; +} + +/* + * Handle an open on 'tasks' file. Prepare a buffer listing the + * process id's of tasks currently attached to the container being opened. + * + * Does not require any specific container mutexes, and does not take any. + */ +static int container_tasks_open(struct inode *unused, struct file *file) +{ + struct container *cont = __d_cont(file->f_dentry->d_parent); + struct ctr_struct *ctr; + pid_t *pidarray; + int npids; + char c; + + if (!(file->f_mode & FMODE_READ)) + return 0; + + ctr = kmalloc(sizeof(*ctr), GFP_KERNEL); + if (!ctr) + goto err0; + + /* + * If container gets more users after we read count, we won't have + * enough space - tough. This race is indistinguishable to the + * caller from the case that the additional container users didn't + * show up until sometime later on. + */ + npids = atomic_read(&cont->count); + pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL); + if (!pidarray) + goto err1; + + npids = pid_array_load(pidarray, npids, cont); + sort(pidarray, npids, sizeof(pid_t), cmppid, NULL); + + /* Call pid_array_to_buf() twice, first just to get bufsz */ + ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1; + ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL); + if (!ctr->buf) + goto err2; + ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids); + + kfree(pidarray); + file->private_data = ctr; + return 0; + +err2: + kfree(pidarray); +err1: + kfree(ctr); +err0: + return -ENOMEM; +} + +static ssize_t container_tasks_read(struct container *cont, + struct cftype *cft, + struct file *file, char __user *buf, + size_t nbytes, loff_t *ppos) +{ + struct ctr_struct *ctr = file->private_data; + + if (*ppos + nbytes > ctr->bufsz) + nbytes = ctr->bufsz - *ppos; + if (copy_to_user(buf, ctr->buf + *ppos, nbytes)) + return -EFAULT; + *ppos += nbytes; + return nbytes; +} + +static int container_tasks_release(struct inode *unused_inode, struct file *file) +{ + struct ctr_struct *ctr; + + if (file->f_mode & FMODE_READ) { + ctr = file->private_data; + kfree(ctr->buf); + kfree(ctr); + } + return 0; +} + +/* + * for the common functions, 'private' gives the type of file + */ + +static struct cftype cft_tasks = { + .name = "tasks", + .open = container_tasks_open, + .read = container_tasks_read, + .write = container_common_file_write, + .release = container_tasks_release, + .private = FILE_TASKLIST, +}; + +static struct cftype cft_notify_on_release = { + .name = "notify_on_release", + .read = container_common_file_read, + .write = container_common_file_write, + .private = FILE_NOTIFY_ON_RELEASE, +}; + +static int container_populate_dir(struct container *cont) +{ + int err; + + if ((err = container_add_file(cont, &cft_notify_on_release)) < 0) + return err; + if ((err = container_add_file(cont, &cft_tasks)) < 0) + return err; + return 0; +} + +/* + * container_create - create a container + * parent: container that will be parent of the new container. + * name: name of the new container. Will be strcpy'ed. + * mode: mode to set on new inode + * + * Must be called with the mutex on the parent inode held + */ + +static long container_create(struct container *parent, const char *name, int mode) +{ + struct container *cont; + int err; + + cont = kmalloc(sizeof(*cont), GFP_KERNEL); + if (!cont) + return -ENOMEM; + + mutex_lock(&manage_mutex); + cont->flags = 0; + if (notify_on_release(parent)) + set_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags); + atomic_set(&cont->count, 0); + INIT_LIST_HEAD(&cont->sibling); + INIT_LIST_HEAD(&cont->children); + + cont->parent = parent; + + mutex_lock(&callback_mutex); + list_add(&cont->sibling, &cont->parent->children); + number_of_containers++; + mutex_unlock(&callback_mutex); + + err = container_create_dir(cont, name, mode); + if (err < 0) + goto err_remove; + + /* + * Release manage_mutex before container_populate_dir() because it + * will down() this new directory's i_mutex and if we race with + * another mkdir, we might deadlock. + */ + mutex_unlock(&manage_mutex); + + err = container_populate_dir(cont); + /* If err < 0, we have a half-filled directory - oh well ;) */ + return 0; + + err_remove: + mutex_lock(&callback_mutex); + list_del(&cont->sibling); + number_of_containers--; + mutex_unlock(&callback_mutex); + + mutex_unlock(&manage_mutex); + kfree(cont); + return err; +} + +static int container_mkdir(struct inode *dir, struct dentry *dentry, int mode) +{ + struct container *c_parent = dentry->d_parent->d_fsdata; + + /* the vfs holds inode->i_mutex already */ + return container_create(c_parent, dentry->d_name.name, mode | S_IFDIR); +} + +/* + * Locking note on the strange update_flag() call below: + * + * If the container being removed is marked cpu_exclusive, then simulate + * turning cpu_exclusive off, which will call update_cpu_domains(). + * The lock_cpu_hotplug() call in update_cpu_domains() must not be + * made while holding callback_mutex. Elsewhere the kernel nests + * callback_mutex inside lock_cpu_hotplug() calls. So the reverse + * nesting would risk an ABBA deadlock. + */ + +static int container_rmdir(struct inode *unused_dir, struct dentry *dentry) +{ + struct container *cont = dentry->d_fsdata; + struct dentry *d; + struct container *parent; + char *pathbuf = NULL; + + /* the vfs holds both inode->i_mutex already */ + + mutex_lock(&manage_mutex); + if (atomic_read(&cont->count) > 0) { + mutex_unlock(&manage_mutex); + return -EBUSY; + } + if (!list_empty(&cont->children)) { + mutex_unlock(&manage_mutex); + return -EBUSY; + } + parent = cont->parent; + mutex_lock(&callback_mutex); + set_bit(CONT_REMOVED, &cont->flags); + list_del(&cont->sibling); /* delete my sibling from parent->children */ + spin_lock(&cont->dentry->d_lock); + d = dget(cont->dentry); + cont->dentry = NULL; + spin_unlock(&d->d_lock); + container_d_remove_dir(d); + dput(d); + number_of_containers--; + mutex_unlock(&callback_mutex); + if (list_empty(&parent->children)) + check_for_release(parent, &pathbuf); + mutex_unlock(&manage_mutex); + container_release_agent(pathbuf); + return 0; +} + +/* + * container_init_early - probably not needed yet, but will be needed + * once cpusets are hooked into this code + */ + +int __init container_init_early(void) +{ + struct task_struct *tsk = current; + + tsk->container = &top_container; + return 0; +} + +/** + * container_init - initialize containers at system boot + * + * Description: Initialize top_container and the container internal file system, + **/ + +int __init container_init(void) +{ + struct dentry *root; + int err; + + init_task.container = &top_container; + + err = register_filesystem(&container_fs_type); + if (err < 0) + goto out; + container_mount = kern_mount(&container_fs_type); + if (IS_ERR(container_mount)) { + printk(KERN_ERR "container: could not mount!\n"); + err = PTR_ERR(container_mount); + container_mount = NULL; + goto out; + } + root = container_mount->mnt_sb->s_root; + root->d_fsdata = &top_container; + root->d_inode->i_nlink++; + top_container.dentry = root; + root->d_inode->i_op = &container_dir_inode_operations; + number_of_containers = 1; + err = container_populate_dir(&top_container); +out: + return err; +} + +/** + * container_fork - attach newly forked task to its parents container. + * @tsk: pointer to task_struct of forking parent process. + * + * Description: A task inherits its parent's container at fork(). + * + * A pointer to the shared container was automatically copied in fork.c + * by dup_task_struct(). However, we ignore that copy, since it was + * not made under the protection of task_lock(), so might no longer be + * a valid container pointer. attach_task() might have already changed + * current->container, allowing the previously referenced container to + * be removed and freed. Instead, we task_lock(current) and copy + * its present value of current->container for our freshly forked child. + * + * At the point that container_fork() is called, 'current' is the parent + * task, and the passed argument 'child' points to the child task. + **/ + +void container_fork(struct task_struct *child) +{ + task_lock(current); + child->container = current->container; + atomic_inc(&child->container->count); + task_unlock(current); +} + +/** + * container_exit - detach container from exiting task + * @tsk: pointer to task_struct of exiting process + * + * Description: Detach container from @tsk and release it. + * + * Note that containers marked notify_on_release force every task in + * them to take the global manage_mutex mutex when exiting. + * This could impact scaling on very large systems. Be reluctant to + * use notify_on_release containers where very high task exit scaling + * is required on large systems. + * + * Don't even think about derefencing 'cont' after the container use count + * goes to zero, except inside a critical section guarded by manage_mutex + * or callback_mutex. Otherwise a zero container use count is a license to + * any other task to nuke the container immediately, via container_rmdir(). + * + * This routine has to take manage_mutex, not callback_mutex, because + * it is holding that mutex while calling check_for_release(), + * which calls kmalloc(), so can't be called holding callback_mutex(). + * + * We don't need to task_lock() this reference to tsk->container, + * because tsk is already marked PF_EXITING, so attach_task() won't + * mess with it, or task is a failed fork, never visible to attach_task. + * + * the_top_container_hack: + * + * Set the exiting tasks container to the root container (top_container). + * + * Don't leave a task unable to allocate memory, as that is an + * accident waiting to happen should someone add a callout in + * do_exit() after the container_exit() call that might allocate. + * If a task tries to allocate memory with an invalid container, + * it will oops in container_update_task_memory_state(). + * + * We call container_exit() while the task is still competent to + * handle notify_on_release(), then leave the task attached to + * the root container (top_container) for the remainder of its exit. + * + * To do this properly, we would increment the reference count on + * top_container, and near the very end of the kernel/exit.c do_exit() + * code we would add a second container function call, to drop that + * reference. This would just create an unnecessary hot spot on + * the top_container reference count, to no avail. + * + * Normally, holding a reference to a container without bumping its + * count is unsafe. The container could go away, or someone could + * attach us to a different container, decrementing the count on + * the first container that we never incremented. But in this case, + * top_container isn't going away, and either task has PF_EXITING set, + * which wards off any attach_task() attempts, or task is a failed + * fork, never visible to attach_task. + * + * Another way to do this would be to set the container pointer + * to NULL here, and check in container_update_task_memory_state() + * for a NULL pointer. This hack avoids that NULL check, for no + * cost (other than this way too long comment ;). + **/ + +void container_exit(struct task_struct *tsk) +{ + struct container *cont; + + cont = tsk->container; + tsk->container = &top_container; /* the_top_container_hack - see above */ + + if (notify_on_release(cont)) { + char *pathbuf = NULL; + + mutex_lock(&manage_mutex); + if (atomic_dec_and_test(&cont->count)) + check_for_release(cont, &pathbuf); + mutex_unlock(&manage_mutex); + container_release_agent(pathbuf); + } else { + atomic_dec(&cont->count); + } +} + +/** + * container_lock - lock out any changes to container structures + * + * The out of memory (oom) code needs to mutex_lock containers + * from being changed while it scans the tasklist looking for a + * task in an overlapping container. Expose callback_mutex via this + * container_lock() routine, so the oom code can lock it, before + * locking the task list. The tasklist_lock is a spinlock, so + * must be taken inside callback_mutex. + */ + +void container_lock(void) +{ + mutex_lock(&callback_mutex); +} + +/** + * container_unlock - release lock on container changes + * + * Undo the lock taken in a previous container_lock() call. + */ + +void container_unlock(void) +{ + mutex_unlock(&callback_mutex); +} + +/* + * proc_container_show() + * - Print tasks container path into seq_file. + * - Used for /proc//container. + * - No need to task_lock(tsk) on this tsk->container reference, as it + * doesn't really matter if tsk->container changes after we read it, + * and we take manage_mutex, keeping attach_task() from changing it + * anyway. No need to check that tsk->container != NULL, thanks to + * the_top_container_hack in container_exit(), which sets an exiting tasks + * container to top_container. + */ +static int proc_container_show(struct seq_file *m, void *v) +{ + struct pid *pid; + struct task_struct *tsk; + char *buf; + int retval; + + retval = -ENOMEM; + buf = kmalloc(PAGE_SIZE, GFP_KERNEL); + if (!buf) + goto out; + + retval = -ESRCH; + pid = m->private; + tsk = get_pid_task(pid, PIDTYPE_PID); + if (!tsk) + goto out_free; + + retval = -EINVAL; + mutex_lock(&manage_mutex); + + retval = container_path(tsk->container, buf, PAGE_SIZE); + if (retval < 0) + goto out_unlock; + seq_puts(m, buf); + seq_putc(m, '\n'); +out_unlock: + mutex_unlock(&manage_mutex); + put_task_struct(tsk); +out_free: + kfree(buf); +out: + return retval; +} + +static int container_open(struct inode *inode, struct file *file) +{ + struct pid *pid = PROC_I(inode)->pid; + return single_open(file, proc_container_show, pid); +} + +struct file_operations proc_container_operations = { + .open = container_open, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, +}; Index: container-2.6.19-rc5/kernel/exit.c =================================================================== --- container-2.6.19-rc5.orig/kernel/exit.c +++ container-2.6.19-rc5/kernel/exit.c @@ -30,6 +30,7 @@ #include #include #include +#include #include #include #include @@ -923,6 +924,7 @@ fastcall NORET_TYPE void do_exit(long co __exit_fs(tsk); exit_thread(); cpuset_exit(tsk); + container_exit(tsk); exit_keys(tsk); if (group_dead && tsk->signal->leader) Index: container-2.6.19-rc5/kernel/fork.c =================================================================== --- container-2.6.19-rc5.orig/kernel/fork.c +++ container-2.6.19-rc5/kernel/fork.c @@ -31,6 +31,7 @@ #include #include #include +#include #include #include #include @@ -1054,6 +1055,7 @@ static struct task_struct *copy_process( p->io_context = NULL; p->io_wait = NULL; p->audit_context = NULL; + container_fork(p); cpuset_fork(p); #ifdef CONFIG_NUMA p->mempolicy = mpol_copy(p->mempolicy); @@ -1287,6 +1289,7 @@ bad_fork_cleanup_policy: bad_fork_cleanup_cpuset: #endif cpuset_exit(p); + container_exit(p); bad_fork_cleanup_delays_binfmt: delayacct_tsk_free(p); if (p->binfmt) Index: container-2.6.19-rc5/kernel/Makefile =================================================================== --- container-2.6.19-rc5.orig/kernel/Makefile +++ container-2.6.19-rc5/kernel/Makefile @@ -36,6 +36,7 @@ obj-$(CONFIG_PM) += power/ obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o obj-$(CONFIG_KEXEC) += kexec.o obj-$(CONFIG_COMPAT) += compat.o +obj-$(CONFIG_CONTAINERS) += container.o obj-$(CONFIG_CPUSETS) += cpuset.o obj-$(CONFIG_IKCONFIG) += configs.o obj-$(CONFIG_STOP_MACHINE) += stop_machine.o Index: container-2.6.19-rc5/Documentation/containers.txt =================================================================== --- /dev/null +++ container-2.6.19-rc5/Documentation/containers.txt @@ -0,0 +1,229 @@ + CONTAINERS + ------- + +Written by Paul Menage based on Documentation/cpusets.txt + +Original copyright in cpusets.txt: +Portions Copyright (C) 2004 BULL SA. +Portions Copyright (c) 2004-2006 Silicon Graphics, Inc. +Modified by Paul Jackson +Modified by Christoph Lameter + +CONTENTS: +========= + +1. Containers + 1.1 What are containers ? + 1.2 Why are containers needed ? + 1.3 How are containers implemented ? + 1.4 What does notify_on_release do ? + 1.5 How do I use containers ? +2. Usage Examples and Syntax + 2.1 Basic Usage + 2.2 Attaching processes +3. Questions +4. Contact + +1. Containers +========== + +1.1 What are containers ? +---------------------- + +Containers provide a mechanism for aggregating sets of tasks, and all +their children, into hierarchical groups. + +Each task has a pointer to a container. Multiple tasks may reference +the same container. User level code may create and destroy containers +by name in the container virtual file system, specify and query to +which container a task is assigned, and list the task pids assigned to +a container. + +On their own, the only use for containers is for simple job +tracking. The intention is that other subsystems, such as cpusets (see +Documentation/cpusets.txt) hook into the generic container support to +provide new attributes for containers, such as accounting/limiting the +resources which processes in a container can access. + +1.2 Why are containers needed ? +---------------------------- + +There are multiple efforts to provide process aggregations in the +Linux kernel, mainly for resource tracking purposes. Such efforts +include cpusets, CKRM/ResGroups, and UserBeanCounters. These all +require the basic notion of a grouping of processes, with newly forked +processes ending in the same group (container) as their parent +process. + +The kernel container patch provides the minimum essential kernel +mechanisms required to efficiently implement such groups. It has +minimal impact on the system fast paths, and provides hooks for +specific subsystems such as cpusets to provide additional behaviour as +desired. + + +1.3 How are containers implemented ? +--------------------------------- + +Containers extends the kernel as follows: + + - Each task in the system is attached to a container, via a pointer + in the task structure to a reference counted container structure. + - The hierarchy of containers can be mounted at /dev/container (or + elsewhere), for browsing and manipulation from user space. + - You can list all the tasks (by pid) attached to any container. + +The implementation of containers requires a few, simple hooks +into the rest of the kernel, none in performance critical paths: + + - in init/main.c, to initialize the root container at system boot. + - in fork and exit, to attach and detach a task from its container. + +In addition a new file system, of type "container" may be mounted, +typically at /dev/container, to enable browsing and modifying the containers +presently known to the kernel. No new system calls are added for +containers - all support for querying and modifying containers is via +this container file system. + +Each task under /proc has an added file named 'container', displaying +the container name, as the path relative to the root of the container file +system. + +Each container is represented by a directory in the container file system +containing the following files describing that container: + + - tasks: list of tasks (by pid) attached to that container + - notify_on_release flag: run /sbin/container_release_agent on exit? + +Other subsystems such as cpusets may add additional files in each +container dir + +New containers are created using the mkdir system call or shell +command. The properties of a container, such as its flags, are +modified by writing to the appropriate file in that containers +directory, as listed above. + +The named hierarchical structure of nested containers allows partitioning +a large system into nested, dynamically changeable, "soft-partitions". + +The attachment of each task, automatically inherited at fork by any +children of that task, to a container allows organizing the work load +on a system into related sets of tasks. A task may be re-attached to +any other container, if allowed by the permissions on the necessary +container file system directories. + +The use of a Linux virtual file system (vfs) to represent the +container hierarchy provides for a familiar permission and name space +for containers, with a minimum of additional kernel code. + +1.4 What does notify_on_release do ? +------------------------------------ + +If the notify_on_release flag is enabled (1) in a container, then whenever +the last task in the container leaves (exits or attaches to some other +container) and the last child container of that container is removed, then +the kernel runs the command /sbin/container_release_agent, supplying the +pathname (relative to the mount point of the container file system) of the +abandoned container. This enables automatic removal of abandoned containers. +The default value of notify_on_release in the root container at system +boot is disabled (0). The default value of other containers at creation +is the current value of their parents notify_on_release setting. + +1.5 How do I use containers ? +-------------------------- + +To start a new job that is to be contained within a container, the steps are: + + 1) mkdir /dev/container + 2) mount -t container container /dev/container + 3) Create the new container by doing mkdir's and write's (or echo's) in + the /dev/container virtual file system. + 4) Start a task that will be the "founding father" of the new job. + 5) Attach that task to the new container by writing its pid to the + /dev/container tasks file for that container. + 6) fork, exec or clone the job tasks from this founding father task. + +For example, the following sequence of commands will setup a container +named "Charlie", containing just CPUs 2 and 3, and Memory Node 1, +and then start a subshell 'sh' in that container: + + mount -t container none /dev/container + cd /dev/container + mkdir Charlie + cd Charlie + /bin/echo $$ > tasks + sh + # The subshell 'sh' is now running in container Charlie + # The next line should display '/Charlie' + cat /proc/self/container + +In the future, a C library interface to containers will likely be +available. For now, the only way to query or modify containers is +via the container file system, using the various cd, mkdir, echo, cat, +rmdir commands from the shell, or their equivalent from C. + +2. Usage Examples and Syntax +============================ + +2.1 Basic Usage +--------------- + +Creating, modifying, using the containers can be done through the container +virtual filesystem. + +To mount it, type: +# mount -t container none /dev/container + +Then under /dev/container you can find a tree that corresponds to the +tree of the containers in the system. For instance, /dev/container +is the container that holds the whole system. + +If you want to create a new container under /dev/container: +# cd /dev/container +# mkdir my_container + +Now you want to do something with this container. +# cd my_container + +In this directory you can find several files: +# ls +notify_on_release tasks + +Now attach your shell to this container: +# /bin/echo $$ > tasks + +You can also create containers inside your container by using mkdir in this +directory. +# mkdir my_sub_cs + +To remove a container, just use rmdir: +# rmdir my_sub_cs +This will fail if the container is in use (has containers inside, or has +processes attached). + +2.2 Attaching processes +----------------------- + +# /bin/echo PID > tasks + +Note that it is PID, not PIDs. You can only attach ONE task at a time. +If you have several tasks to attach, you have to do it one after another: + +# /bin/echo PID1 > tasks +# /bin/echo PID2 > tasks + ... +# /bin/echo PIDn > tasks + + +3. Questions +============ + +Q: what's up with this '/bin/echo' ? +A: bash's builtin 'echo' command does not check calls to write() against + errors. If you use it in the container file system, you won't be + able to tell whether a command succeeded or failed. + +Q: When I attach processes, only the first of the line gets really attached ! +A: We can only return one error code per call to write(). So you should also + put only ONE pid. + --