[RFC PATCH 5/5] use next syscall data to predefine the file descriptor value

[Nadia Derbey]

kathys wrote:
> Hi Nadia,
> 
> I am trying with great difficulty to incorporate these patches into the 
> existing lxc-tree on 2.6.26-rc8-mm1-lxc1, they are conflicting with a 
> number of other patches from checkpoint/.

Kathy,

Is it the same problem as the one we have solved by private e-mail?

Regards,
Nadia

> Serge has asked me to include 
> them in the next lxc release so I need to know how to make them fit.
> 
> I will put out 2.6.26-rc8-mm1-lxc1 without your patches because its 
> taking me too long, I will endeavor to include them in the 
> 2.6.26-rc8-mm1-lxc2, so if you could have a look at them against the 
> next release of lxc which I hope to get out by tomorrow (Thursday) 
> afternoon.
> 
> Thanks,
> 
> Kathy
> 
> Serge E. Hallyn wrote:
> 
>> Quoting Nadia.Derbey at bull.net (Nadia.Derbey at bull.net):
>>  
>>
>>> [PATCH 05/05]
>>>
>>> This patch uses the value written into the next_syscall_data proc file
>>> as a target file descriptor for the next file to be opened.
>>>
>>> This makes it easy to restart a process with the same fds as the ones 
>>> it was
>>> using during the checkpoint phase, instead of 1. opening the file, 2. 
>>> dup2'ing
>>> the open file descriptor.
>>>
>>> The following syscalls are impacted if next_syscall_data is set:
>>> . open()
>>> . openat()
>>>     
>>
>>
>> Oh, neat, I somehow missed the fact that you had this in your previous
>> posting  :)
>>
>>  
>>
>>> Signed-off-by: Nadia Derbey <Nadia.Derbey at bull.net>
>>>     
>>
>>
>> It'd be nice if the get_predefined_fd_flags() could share a helper
>> with get_unused_fd_flags() (in particular because the "/* snaity check */
>> at the end is between a '#if 1' which sounds like it may one day be
>> removed), but I'm not sure offhand the best way to do that.  So for now
>>
>> Acked-by: Serge Hallyn <serue at us.ibm.com>
>>
>> Thanks, Nadia.
>>
>> Kathy, I'd love to see a -lxc release with this patchset so we can test
>> it with cryo.
>>
>> Suka, the open with specified id here might help your simplify your pipe
>> c/r patches for cryo?
>>
>> -serge
>>
>>  
>>
>>> ---
>>>  fs/open.c |   62 
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>>  1 file changed, 61 insertions(+), 1 deletion(-)
>>>
>>> Index: linux-2.6.26-rc8-mm1/fs/open.c
>>> ===================================================================
>>> --- linux-2.6.26-rc8-mm1.orig/fs/open.c    2008-07-08 
>>> 12:12:34.000000000 +0200
>>> +++ linux-2.6.26-rc8-mm1/fs/open.c    2008-07-08 13:23:03.000000000 
>>> +0200
>>> @@ -974,6 +974,59 @@ struct file *dentry_open(struct dentry *
>>>  EXPORT_SYMBOL(dentry_open);
>>>
>>>  /*
>>> + * Marks a given file descriptor entry as busy (should not be busy 
>>> when this
>>> + * routine is called.
>>> + *
>>> + * files->next_fd is not updated: this lets the potentially created 
>>> hole be
>>> + * filled up on next calls to get_unused_fd_flags.
>>> + *
>>> + * Returns the specified fd if successful, -errno else.
>>> + */
>>> +static int get_predefined_fd_flags(int fd, int flags)
>>> +{
>>> +    struct files_struct *files = current->files;
>>> +    int error;
>>> +    struct fdtable *fdt;
>>> +
>>> +    error = -EINVAL;
>>> +    if (fd < 0)
>>> +        goto out;
>>> +
>>> +    error = -EMFILE;
>>> +    if (fd >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
>>> +        goto out;
>>> +
>>> +    spin_lock(&files->file_lock);
>>> +    fdt = files_fdtable(files);
>>> +
>>> +    error = expand_files(files, fd);
>>> +    if (error < 0)
>>> +        goto out_unlock;
>>> +
>>> +    error = -EBUSY;
>>> +    if (FD_ISSET(fd, fdt->open_fds))
>>> +        goto out_unlock;
>>> +
>>> +    FD_SET(fd, fdt->open_fds);
>>> +    if (flags & O_CLOEXEC)
>>> +        FD_SET(fd, fdt->close_on_exec);
>>> +    else
>>> +        FD_CLR(fd, fdt->close_on_exec);
>>> +
>>> +    /* Sanity check */
>>> +    if (fdt->fd[fd] != NULL) {
>>> +        printk(KERN_WARNING "get_unused_fd: slot %d not NULL!\n", fd);
>>> +        fdt->fd[fd] = NULL;
>>> +    }
>>> +
>>> +    error = fd;
>>> +out_unlock:
>>> +    spin_unlock(&files->file_lock);
>>> +out:
>>> +    return error;
>>> +}
>>> +
>>> +/*
>>>   * Find an empty file descriptor entry, and mark it busy.
>>>   */
>>>  int get_unused_fd_flags(int flags)
>>> @@ -1088,7 +1141,14 @@ long do_sys_open(int dfd, const char __u
>>>      int fd = PTR_ERR(tmp);
>>>
>>>      if (!IS_ERR(tmp)) {
>>> -        fd = get_unused_fd_flags(flags);
>>> +        if (unlikely(next_data_set(current))) {
>>> +            int next_fd = get_next_data(current);
>>> +
>>> +            fd = get_predefined_fd_flags(next_fd, flags);
>>> +            reset_next_syscall_data(current);
>>> +        } else
>>> +            fd = get_unused_fd_flags(flags);
>>> +
>>>          if (fd >= 0) {
>>>              struct file *f = do_filp_open(dfd, tmp, flags, mode);
>>>              if (IS_ERR(f)) {
>>>
>>> -- 
>>>     
>>
>>
>>   
> 
> 
> 
> 


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