Re: [RFC][PATCH v2 4/4] vfs: wrap write f_ops with file_{start,end}_write()

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

On 01/28/2017 05:20 AM, Amir Goldstein wrote:
> On Fri, Jan 27, 2017 at 1:50 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>> On Fri, Jan 27, 2017 at 1:09 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>>> On Mon, Jan 23, 2017 at 8:43 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>>>> Before calling write f_ops, call file_start_write() instead
>>>> of sb_start_write().
>>>>
>>>> This ensures freeze protection for both overlay and upper fs
>>>> when file is open from an overlayfs mount.
>>>>
>>>> Replace {sb,file}_start_write() for {copy,clone}_file_range() and
>>>> for fallocate().
>>>>
>>>> For dedup_file_range() there is no need for mnt_want_write_file().
>>>> File is already open for write, so we already have mnt_want_write()
>>>> and we only need file_start_write().
>>>
>>> Being opened for write is not verified if capable(CAP_SYS_ADMIN).
>>> Ugly special case, don't ask me why it's done...
>>>
>>
>> Christoph, Darrick, is that by design?
> 
> Anyway, whether is makes sense or not, that's a legacy from
> BTRFS_IOC_FILE_EXTENT_SAME, we probably have to live with.
> 
> Michael, I recon man page needs updating.

Sorry--can you elaborate on what changes are required?

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/