Re: [RFC PATCH 2/6] IPC/sem: per <pid> semundo file in procfs

[Nadia Derbey <Nadia.Derbey-6ktuUTfB/bM@public.gmane.org>]

Michael Kerrisk wrote:
> On 6/25/08, Nadia.Derbey-6ktuUTfB/bM@public.gmane.org <Nadia.Derbey-6ktuUTfB/bM@public.gmane.org> 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-6ktuUTfB/bM@public.gmane.org>
>> Signed-off-by: Nadia Derbey <Nadia.Derbey-6ktuUTfB/bM@public.gmane.org>
> 
> 
> 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
>>
>>
>> --
>> _______________________________________________
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>> https://lists.linux-foundation.org/mailman/listinfo/containers
>>
> 
> 
> 


-- 
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Name.......... Nadia DERBEY
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