[Devel] Re: [RFC][PATCH 4/4] introduce proc_mnt for pid_ns

sukadev at us.ibm.com sukadev at us.ibm.com
Thu Feb 1 20:17:05 PST 2007


Dave Hansen [hansendc at us.ibm.com] wrote:
| 
| The following patch completes the removal of proc_mnt.  It fetches
| the mnt on which to do dentry invalidations from the pid_namespace
| in which the task appears.
| 
| For now, there is only one pid namespace in mainline so this is
| straightforward.  In the -lxc tree we'll have to do something
| more complex.
| 
| Note that the new proc_compare_super() enforces the "one proc sb
| per pid_namespace" limit.
| 
| ---
| 
|  lxc-dave/fs/proc/base.c                |   26 ++++++++++++++++++++++--
|  lxc-dave/fs/proc/inode.c               |    2 -
|  lxc-dave/fs/proc/root.c                |   35 ++++++++++++++++++++++++++-------
|  lxc-dave/include/linux/pid_namespace.h |    1 
|  lxc-dave/include/linux/proc_fs.h       |    1 
|  5 files changed, 53 insertions(+), 12 deletions(-)
| 
| diff -puN fs/proc/base.c~A3-remove-proc_mnt-1 fs/proc/base.c
| --- lxc/fs/proc/base.c~A3-remove-proc_mnt-1	2007-01-26 14:29:18.000000000 -0800
| +++ lxc-dave/fs/proc/base.c	2007-01-26 14:29:18.000000000 -0800
| @@ -70,6 +70,7 @@
|  #include <linux/seccomp.h>
|  #include <linux/cpuset.h>
|  #include <linux/audit.h>
| +#include <linux/pid_namespace.h>
|  #include <linux/poll.h>
|  #include <linux/nsproxy.h>
|  #include <linux/oom.h>
| @@ -1905,9 +1906,11 @@ static struct inode_operations proc_tgid
|  };
|  
|  /**
| - * proc_flush_task -  Remove dcache entries for @task from the /proc dcache.
| + * proc_flush_task_from_pid_ns -  Remove dcache entries for @task
| + * 				  from the /proc dcache.
|   *
|   * @task: task that should be flushed.
| + * @pid_ns: pid_namespace in which that task appears
|   *
|   * Looks in the dcache for
|   * /proc/@pid
| @@ -1925,11 +1928,20 @@ static struct inode_operations proc_tgid
|   *       that no dcache entries will exist at process exit time it
|   *       just makes it very unlikely that any will persist.
|   */
| -void proc_flush_task(struct task_struct *task)
| +void proc_flush_task_from_pid_ns(struct task_struct *task,
| +				struct pid_namespace* pid_ns)
|  {
|  	struct dentry *dentry, *leader, *dir;
|  	char buf[PROC_NUMBUF];
|  	struct qstr name;
| +	struct vfsmount *proc_mnt = pid_ns->proc_mnt;
| +
| +	/*
| +	 * It is possible that no /procs have been instantiated
| +	 * for this particular pid namespace.
| +	 */
| +	if (!proc_mnt)
| +		return;
|  
|  	name.name = buf;
|  	name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
| @@ -1971,6 +1983,16 @@ out:
|  	return;
|  }
|  
| +void proc_flush_task(struct task_struct *task)
| +{
| +	/*
| +	 * Right now, tasks only appear in their own pid_ns.
| +	 * With containers this function will change to a loop
| +	 * over all pid_ns's in which the task appears.
| +	 */
| +	proc_flush_task_from_pid_ns(task, current->nsproxy->pid_ns);
| +}
| +
|  static struct dentry *proc_pid_instantiate(struct inode *dir,
|  					   struct dentry * dentry,
|  					   struct task_struct *task, void *ptr)
| diff -puN fs/proc/inode.c~A3-remove-proc_mnt-1 fs/proc/inode.c
| --- lxc/fs/proc/inode.c~A3-remove-proc_mnt-1	2007-01-26 14:29:18.000000000 -0800
| +++ lxc-dave/fs/proc/inode.c	2007-01-26 14:29:18.000000000 -0800
| @@ -67,8 +67,6 @@ static void proc_delete_inode(struct ino
|  	clear_inode(inode);
|  }
|  
| -struct vfsmount *proc_mnt;
| -
|  static void proc_read_inode(struct inode * inode)
|  {
|  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
| diff -puN fs/proc/root.c~A3-remove-proc_mnt-1 fs/proc/root.c
| --- lxc/fs/proc/root.c~A3-remove-proc_mnt-1	2007-01-26 14:29:18.000000000 -0800
| +++ lxc-dave/fs/proc/root.c	2007-01-26 14:29:18.000000000 -0800
| @@ -18,6 +18,7 @@
|  #include <linux/bitops.h>
|  #include <linux/smp_lock.h>
|  #include <linux/mount.h>
| +#include <linux/pid_namespace.h>
|  
|  #include "internal.h"
|  
| @@ -27,10 +28,36 @@ struct proc_dir_entry *proc_net, *proc_n
|  struct proc_dir_entry *proc_sys_root;
|  #endif
|  
| +static int proc_compare_super(struct super_block *s, void *p)
| +{
| +	struct pid_namespace *pid_ns = p;
| +	if (pid_ns->proc_mnt->mnt_sb == s)
| +		return 1;
| +	return 0;
| +}
| +
|  static int proc_get_sb(struct file_system_type *fs_type,
|  	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
|  {
| -	return get_sb_single(fs_type, flags, data, proc_fill_super, mnt);
| +	struct super_block *s;
| +
| +	struct pid_namespace *pid_ns = current->nsproxy->pid_ns;
| +	int error;
| +
| +	s = sget(fs_type, proc_compare_super, set_anon_super, pid_ns);
| +	if (IS_ERR(s))
| +		return PTR_ERR(s);
| +	if (!pid_ns->proc_mnt)
| +		pid_ns->proc_mnt = mnt;
| +
| +	error = fill_if_new_sb(s, pid_ns, flags, proc_fill_super);
| +	if (error)
| +		return error;
| +
| +	do_remount_sb(s, flags, data, 0);
| +	error = simple_set_mnt(mnt, s);
| +
| +	return error;
|  }
|  
|  static struct file_system_type proc_fs_type = {
| @@ -47,12 +74,6 @@ void __init proc_root_init(void)
|  	err = register_filesystem(&proc_fs_type);
|  	if (err)
|  		return;
| -	proc_mnt = kern_mount(&proc_fs_type);
| -	err = PTR_ERR(proc_mnt);
| -	if (IS_ERR(proc_mnt)) {
| -		unregister_filesystem(&proc_fs_type);
| -		return;
| -	}

If we remove the kern_mount() call here, where do we mount
/proc for the init_pid_ns now ? i.e how does proc_get_sb()
get called the first time ?


|  	proc_misc_init();
|  	proc_net = proc_mkdir("net", NULL);
|  	proc_net_stat = proc_mkdir("net/stat", NULL);
| diff -puN include/linux/pid_namespace.h~A3-remove-proc_mnt-1 include/linux/pid_namespace.h
| --- lxc/include/linux/pid_namespace.h~A3-remove-proc_mnt-1	2007-01-26 14:29:18.000000000 -0800
| +++ lxc-dave/include/linux/pid_namespace.h	2007-01-26 14:29:18.000000000 -0800
| @@ -20,6 +20,7 @@ struct pid_namespace {
|  	struct pidmap pidmap[PIDMAP_ENTRIES];
|  	int last_pid;
|  	struct task_struct *child_reaper;
| +	struct vfsmount *proc_mnt;
|  };
|  
|  extern struct pid_namespace init_pid_ns;
| diff -puN include/linux/proc_fs.h~A3-remove-proc_mnt-1 include/linux/proc_fs.h
| --- lxc/include/linux/proc_fs.h~A3-remove-proc_mnt-1	2007-01-26 14:29:18.000000000 -0800
| +++ lxc-dave/include/linux/proc_fs.h	2007-01-26 14:29:18.000000000 -0800
| @@ -109,7 +109,6 @@ extern struct proc_dir_entry *create_pro
|  						struct proc_dir_entry *parent);
|  extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
|  
| -extern struct vfsmount *proc_mnt;
|  extern int proc_fill_super(struct super_block *,void *,int);
|  extern struct inode *proc_get_inode(struct super_block *, unsigned int, struct proc_dir_entry *);
|  
| _
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