Quoting [EMAIL PROTECTED] ([EMAIL PROTECTED]):
> PATCH [02/06]
>
> This patch adds a new procfs interface to display the per-process semundo
> data.
>
> A new per-PID file is added, called "semundo".
> It contains one line per semaphore IPC where there is something to undo for
> this process.
> Then, each line contains the semid followed by each undo value
> corresponding to each semaphores of the semaphores array.
>
> This interface will be particularly useful to allow a user access
> these data, for example for checkpointing a process
>
> With this patch, the semundo file can only be accessed in read mode.
> When this file is opened, if an undo_list exists for the target process, it
> is accessed in an rcu read section, and its refcount is incremented, avoiding
> that it be freed.
> The reverse is done during the release operation, and the undo_list is
> freed if the process reading the file was the last process accessing that
> list.
>
> Signed-off-by: Pierre Peiffer <[EMAIL PROTECTED]>
> Signed-off-by: Nadia Derbey <[EMAIL PROTECTED]>
Acked-by: Serge Hallyn <[EMAIL PROTECTED]>
-serge
>
> ---
> fs/proc/base.c | 3 +
> fs/proc/internal.h | 1
> ipc/sem.c | 127
> +++++++++++++++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 128 insertions(+), 3 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 09:05:09.000000000
> +0200
> +++ linux-2.6.26-rc5-mm3/fs/proc/base.c 2008-06-24 10:03:33.000000000
> +0200
> @@ -2525,6 +2525,9 @@ static const struct pid_entry tgid_base_
> #ifdef CONFIG_TASK_IO_ACCOUNTING
> INF("io", S_IRUGO, tgid_io_accounting),
> #endif
> +#ifdef CONFIG_SYSVIPC
> + REG("semundo", S_IRUGO, semundo),
> +#endif
> };
>
> static int proc_tgid_base_readdir(struct file * filp,
> Index: linux-2.6.26-rc5-mm3/fs/proc/internal.h
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/fs/proc/internal.h 2008-06-24
> 09:05:09.000000000 +0200
> +++ linux-2.6.26-rc5-mm3/fs/proc/internal.h 2008-06-24 10:04:19.000000000
> +0200
> @@ -65,6 +65,7 @@ extern const struct file_operations proc
> extern const struct file_operations proc_net_operations;
> extern const struct file_operations proc_kmsg_operations;
> extern const struct inode_operations proc_net_inode_operations;
> +extern const struct file_operations proc_semundo_operations;
>
> void free_proc_entry(struct proc_dir_entry *de);
>
> Index: linux-2.6.26-rc5-mm3/ipc/sem.c
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/ipc/sem.c 2008-06-24 09:37:33.000000000
> +0200
> +++ linux-2.6.26-rc5-mm3/ipc/sem.c 2008-06-24 10:59:46.000000000 +0200
> @@ -97,6 +97,7 @@ static void freeary(struct ipc_namespace
> #ifdef CONFIG_PROC_FS
> static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
> #endif
> +static void free_semundo_list(struct sem_undo_list *, struct ipc_namespace
> *);
>
> #define SEMMSL_FAST 256 /* 512 bytes on stack */
> #define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
> @@ -1282,8 +1283,14 @@ void exit_sem(struct task_struct *tsk)
> rcu_assign_pointer(tsk->sysvsem.undo_list, NULL);
> synchronize_rcu();
>
> - if (!atomic_dec_and_test(&ulp->refcnt))
> - return;
> + if (atomic_dec_and_test(&ulp->refcnt))
> + free_semundo_list(ulp, tsk->nsproxy->ipc_ns);
> +}
> +
> +static void free_semundo_list(struct sem_undo_list *ulp,
> + struct ipc_namespace *ipc_ns)
> +{
> + BUG_ON(atomic_read(&ulp->refcnt));
>
> for (;;) {
> struct sem_array *sma;
> @@ -1303,7 +1310,7 @@ void exit_sem(struct task_struct *tsk)
> if (semid == -1)
> break;
>
> - sma = sem_lock_check(tsk->nsproxy->ipc_ns, un->semid);
> + sma = sem_lock_check(ipc_ns, un->semid);
>
> /* exit_sem raced with IPC_RMID, nothing to do */
> if (IS_ERR(sma))
> @@ -1384,4 +1391,118 @@ static int sysvipc_sem_proc_show(struct
> sma->sem_otime,
> sma->sem_ctime);
> }
> +
> +struct undo_list_data {
> + struct sem_undo_list *undo_list;
> + struct ipc_namespace *ipc_ns;
> +};
> +
> +/* iterator */
> +static void *semundo_start(struct seq_file *m, loff_t *ppos)
> +{
> + return NULL;
> +}
> +
> +static void *semundo_next(struct seq_file *m, void *v, loff_t *ppos)
> +{
> + return NULL;
> +}
> +
> +static void semundo_stop(struct seq_file *m, void *v)
> +{
> + return;
> +}
> +
> +static int semundo_show(struct seq_file *m, void *v)
> +{
> + return 0;
> +}
> +
> +static struct seq_operations semundo_op = {
> + .start = semundo_start,
> + .next = semundo_next,
> + .stop = semundo_stop,
> + .show = semundo_show
> +};
> +
> +static struct sem_undo_list *get_proc_ulp(struct task_struct *tsk)
> +{
> + struct sem_undo_list *ulp;
> +
> + rcu_read_lock();
> + ulp = rcu_dereference(tsk->sysvsem.undo_list);
> + if (ulp)
> + if (!atomic_inc_not_zero(&ulp->refcnt))
> + ulp = NULL;
> + rcu_read_unlock();
> + return ulp;
> +}
> +
> +static void put_proc_ulp(struct sem_undo_list *ulp,
> + struct ipc_namespace *ns)
> +{
> + if (ulp && atomic_dec_and_test(&ulp->refcnt))
> + free_semundo_list(ulp, ns);
> +}
> +
> +/*
> + * semundo_open: open operation for /proc/<PID>/semundo file
> + */
> +static int semundo_open(struct inode *inode, struct file *file)
> +{
> + struct task_struct *task;
> + struct sem_undo_list *ulp;
> + struct undo_list_data *data;
> + struct ipc_namespace *ns;
> + int ret = 0;
> +
> + data = kzalloc(sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + task = get_pid_task(PROC_I(inode)->pid, PIDTYPE_PID);
> + if (!task) {
> + ret = -EINVAL;
> + goto out_err;
> + }
> +
> + ulp = get_proc_ulp(task);
> + ns = get_ipc_ns(task->nsproxy->ipc_ns);
> + put_task_struct(task);
> +
> + ret = seq_open(file, &semundo_op);
> + if (!ret) {
> + struct seq_file *m = file->private_data;
> + data->undo_list = ulp;
> + data->ipc_ns = ns;
> + m->private = data;
> + return 0;
> + }
> +
> + put_proc_ulp(ulp, ns);
> + put_ipc_ns(ns);
> +out_err:
> + kfree(data);
> + return ret;
> +}
> +
> +static int semundo_release(struct inode *inode, struct file *file)
> +{
> + struct seq_file *m = file->private_data;
> + struct undo_list_data *data = m->private;
> + struct sem_undo_list *ulp = data->undo_list;
> + struct ipc_namespace *ns = data->ipc_ns;
> +
> + put_proc_ulp(ulp, ns);
> + put_ipc_ns(ns);
> + kfree(data);
> + return seq_release(inode, file);
> +}
> +
> +const struct file_operations proc_semundo_operations = {
> + .open = semundo_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = semundo_release,
> +};
> #endif
>
> --
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