Michael Kerrisk wrote:
> On 6/25/08, Nadia.Derbey@xxxxxxxx <Nadia.Derbey@xxxxxxxx> wrote:
>
>>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 <pierre.peiffer@xxxxxxxx>
>> Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
>
>
> Nadia,
>
> This is a kernel-userland interface change, please do CC me, so that I
> can change the man pages if needed.
So sorry Michael, but looks like I forgot the complete documentation
part: I also have an issue from Serge about a missing documentation in
the Documentation directory.
Will fix that and take that opportunity to put you in the loop.
Regards,
Nadia
>
> Cheers,
>
> Michael
>
>
>
>
>> ---
>> 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
>>
>>
>> --
>> _______________________________________________
>> Containers mailing list
>> Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> https://lists.linux-foundation.org/mailman/listinfo/containers
>>
>
>
>
--
===============================================================
Name.......... Nadia DERBEY
Organization.. BULL/DT/OSwR&D/Linux
---------------------------------------------------------------
Email......... mailto:Nadia.Derbey@xxxxxxxx
Address....... BULL, B.P. 208, 38432 Echirolles Cedex, France
Tel........... (33) 76 29 77 62 [Internal Bull: (229) 77 62]
Telex,Fax..... 980648 F - (33) 76 29 76 00
Internal Bull. Mail: FREC-B1208
===============================================================
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