[RFC PATCH 6/6] IPC/sem: .write operation for /proc/<self>/semundo
Nadia Derbey
Nadia.Derbey at bull.net
Wed Jun 25 22:44:25 PDT 2008
Serge E. Hallyn wrote:
> Quoting Nadia.Derbey at bull.net (Nadia.Derbey at bull.net):
>
>>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'.
>
>
> There should also be a patch against Documentation/filesystems/proc.txt
>
Ok, will do that.
>
>>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.
>>+ */
>
>
> (I'll probably regret asking this when I turn out to be obviously wrong,
> but:)
>
> What if I'm opening the file O_RDWR and first read the file? You'll end
> up showing no entries, right?
Yes, exactly. I know this is weird, and I 1st thought of delaying the
check on task = current until the actual .write operation. But it would
have made things a bit more complicated:
. add the task pointer to the private data
. delay the put_task_struct
>
> Which may be ok, so long as it's properly documented in proc.txt...
Ok, will do that
>
> thanks,
> -serge
>
>
>>+ 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,
>> };
>>
>>--
>
>
>
More information about the Containers
mailing list