[Devel] [RFC PATCH 6/6] IPC/sem: .write operation for /proc/<self>/semundo
Nadia.Derbey at bull.net
Nadia.Derbey at bull.net
Wed Jun 25 06:49:16 PDT 2008
PATCH [06/06]
This patch introduces the .write seq operation for /proc/pid/semundo.
In order to simplify the locking strategy, the write operation is only allowed
to 'current'.
Signed-off-by: Nadia Derbey <Nadia.Derbey at bull.net>
---
fs/proc/base.c | 2
ipc/sem.c | 250 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 250 insertions(+), 2 deletions(-)
Index: linux-2.6.26-rc5-mm3/fs/proc/base.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/fs/proc/base.c 2008-06-24 10:03:33.000000000 +0200
+++ linux-2.6.26-rc5-mm3/fs/proc/base.c 2008-06-24 13:21:44.000000000 +0200
@@ -2526,7 +2526,7 @@ static const struct pid_entry tgid_base_
INF("io", S_IRUGO, tgid_io_accounting),
#endif
#ifdef CONFIG_SYSVIPC
- REG("semundo", S_IRUGO, semundo),
+ REG("semundo", S_IWUSR|S_IRUGO, semundo),
#endif
};
Index: linux-2.6.26-rc5-mm3/ipc/sem.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/ipc/sem.c 2008-06-24 12:59:15.000000000 +0200
+++ linux-2.6.26-rc5-mm3/ipc/sem.c 2008-06-25 08:56:07.000000000 +0200
@@ -1554,7 +1554,27 @@ static int semundo_open(struct inode *in
goto out_err;
}
- ulp = get_proc_ulp(task);
+ if (file->f_flags & O_WRONLY || file->f_flags & O_RDWR) {
+ /*
+ * Writing is only allowed to current
+ */
+ if (task != current) {
+ put_task_struct(task);
+ ret = -EPERM;
+ goto out_err;
+ }
+ /*
+ * No need to increment the undo_list's refcnt: only current
+ * can be freeing it through exit, and we are current.
+ * Only signal through the ulp NULL pointer that it won't be
+ * necessary to decrement the refcnt during release.
+ * Actually, in this path the undo_list will be gotten during
+ * the write operation.
+ */
+ ulp = NULL;
+ } else
+ ulp = get_proc_ulp(task);
+
ns = get_ipc_ns(task->nsproxy->ipc_ns);
put_task_struct(task);
@@ -1574,6 +1594,233 @@ out_err:
return ret;
}
+/* Skip all spaces at the beginning of the buffer */
+static inline int skip_space(const char __user **buf, size_t *len)
+{
+ char c = 0;
+ while (*len) {
+ if (get_user(c, *buf))
+ return -EFAULT;
+ if (c != '\t' && c != ' ')
+ break;
+ --*len;
+ ++*buf;
+ }
+ return c;
+}
+
+/* Retrieve the first numerical value contained in the string.
+ * Note: The value is supposed to be a 32-bit integer.
+ */
+static inline int get_next_value(const char __user **buf, size_t *len, int *val)
+{
+#define BUFLEN 11
+ int err, neg = 0, left;
+ char s[BUFLEN], *p;
+
+ err = skip_space(buf, len);
+ if (err < 0)
+ return err;
+ if (!*len)
+ return INT_MAX;
+ if (err == '\n') {
+ ++*buf;
+ --*len;
+ return INT_MAX;
+ }
+ if (err == '-') {
+ ++*buf;
+ --*len;
+ neg = 1;
+ }
+
+ left = *len;
+ if (left > sizeof(s) - 1)
+ left = sizeof(s) - 1;
+ if (copy_from_user(s, *buf, left))
+ return -EFAULT;
+
+ s[left] = 0;
+ p = s;
+ if (*p < '0' || *p > '9')
+ return -EINVAL;
+
+ *val = simple_strtoul(p, &p, 0);
+ if (neg)
+ *val = -(*val);
+
+ left = p-s;
+ (*len) -= left;
+ (*buf) += left;
+
+ return 0;
+#undef BUFLEN
+}
+
+/*
+ * Reads a line from /proc/self/semundo.
+ * Returns the number of undo values read (or errcode upon failure).
+ * @id: pointer to the semid (filled in with 1st field in the line)
+ * @array: semundo values (filled in iwth remaining fields in the line).
+ * @array_len: max # of expected semundo values
+ */
+static inline int semundo_readline(const char __user **buf, size_t *left,
+ int *id, short *array, int array_len)
+{
+ int i, val, err;
+
+ /* Read semid */
+ err = get_next_value(buf, left, id);
+ if (err)
+ return err;
+
+ /* Read all (semundo-) values of a full line */
+ for (i = 0; ; i++) {
+ err = get_next_value(buf, left, &val);
+ if (err < 0)
+ return err;
+ /* reached end of line or end of buffer */
+ if (err == INT_MAX)
+ break;
+ /* Return an error if we get more values than expected */
+ if (i < array_len)
+ array[i] = val;
+ else
+ return -EINVAL;
+ }
+ return i;
+}
+
+/*
+ * sets or updates the undo values for the undo_list of a given semaphore id.
+ * This is exactly the same code sequence as sys_semtimedop if we have undos.
+ */
+static inline int semundo_update(struct ipc_namespace *ns, int semid,
+ short *array, int size)
+{
+ struct sem_undo *un;
+ struct sem_array *sma;
+ int ret = 0;
+
+ un = find_alloc_undo(ns, semid);
+ if (IS_ERR(un)) {
+ ret = PTR_ERR(un);
+ goto out;
+ }
+
+ /* lookup the sem_array */
+ sma = sem_lock(ns, semid);
+ if (IS_ERR(sma)) {
+ ret = PTR_ERR(sma);
+ rcu_read_unlock();
+ goto out;
+ }
+
+ /*
+ * find_alloc_undo opened an rcu read section to protect un.
+ * Releasing it here is safe:
+ * . sem_lock is held, so we are protected against IPC_RMID
+ * . the refcnt won't fall to 0 since exit_sem only operates on
+ * current and we are the current.
+ */
+ rcu_read_unlock();
+
+ /*
+ * semid identifiers are not unique - find_alloc_undo() may have
+ * allocated an undo structure, it was invalidated by an RMID and now
+ * a new array received the same id.
+ * Check and fail.
+ * This case can be detected checking un->semid. The existance of
+ * "un" itself is guaranteed by rcu.
+ */
+ if (un->semid == -1) {
+ ret = -EIDRM;
+ goto out_unlock;
+ }
+
+ /*
+ * If the number of values given does not match the number of
+ * semaphores in the array, consider this as an error.
+ */
+ if (size != sma->sem_nsems) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ /* update the undo values */
+ while (--size >= 0)
+ un->semadj[size] = array[size];
+
+ /* maybe some queued-up processes were waiting for this */
+ update_queue(sma);
+
+out_unlock:
+ sem_unlock(sma);
+out:
+ return ret;
+}
+
+/*
+ * write operation for /proc/self/semundo file
+ *
+ * Only current is allowed to write to its semundo file.
+ *
+ * The expected string format is:
+ * "<semID> <val1> <val2> ... <valN>"
+ *
+ * It sets (or updates) the sem_undo list for 'current' and the target
+ * <semID>, to the given 'undo' values.
+ *
+ * <semID> must match an existing semaphore array.
+ * The number of values following <semID> must match the number of semaphores
+ * in the corresponding array.
+ *
+ * Multiple semID's can be passed simultaneously: newline ('\n') is considered
+ * as a separator in that case.
+ *
+ * Note: it is not allowed to set the sem_undo list for a given semID using
+ * mutliple write calls.
+ */
+static ssize_t semundo_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct seq_file *m = file->private_data;
+ short *array;
+ int err, max_sem, semid = 0;
+ size_t left = count;
+ struct undo_list_data *data = m->private;
+ struct ipc_namespace *ns = data->ipc_ns;
+
+ if (data->undo_list)
+ /* Should never happen */
+ return -EINVAL;
+
+ max_sem = ns->sc_semmsl;
+
+ array = kmalloc(sizeof(short)*max_sem, GFP_KERNEL);
+ if (array == NULL)
+ return -ENOMEM;
+
+ while (left) {
+ int nval;
+
+ nval = semundo_readline(&buf, &left, &semid, array, max_sem);
+ if (nval < 0) {
+ err = nval;
+ goto out;
+ }
+
+ err = semundo_update(ns, semid, array, nval);
+ if (err)
+ goto out;
+ }
+ err = count - left;
+
+out:
+ kfree(array);
+ return err;
+}
+
static int semundo_release(struct inode *inode, struct file *file)
{
struct seq_file *m = file->private_data;
@@ -1590,6 +1837,7 @@ static int semundo_release(struct inode
const struct file_operations proc_semundo_operations = {
.open = semundo_open,
.read = seq_read,
+ .write = semundo_write,
.llseek = seq_lseek,
.release = semundo_release,
};
--
_______________________________________________
Containers mailing list
Containers at lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers
More information about the Devel
mailing list