[PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open syscall
piastry at etersoft.ru
Tue Feb 5 05:45:31 CST 2013
2013/1/31 J. Bruce Fields <bfields at fieldses.org>:
> On Thu, Jan 17, 2013 at 08:52:59PM +0400, Pavel Shilovsky wrote:
>> If O_DENYMAND flag is specified, O_DENYREAD/WRITE/MAND flags are
>> translated to flock's flags:
>> !O_DENYREAD -> LOCK_READ
>> !O_DENYWRITE -> LOCK_WRITE
>> O_DENYMAND -> LOCK_MAND
>> and set through flock_lock_file on a file.
>> This change only affects opens that use O_DENYMAND flag - all other
>> native Linux opens don't care about these flags. It allow us to
>> enable this feature for applications that need it (e.g. NFS and
>> Samba servers that export the same directory for Windows clients,
>> or Wine applications that access the same files simultaneously).
> The use of an is_conflict callback seems unnecessarily convoluted.
> If we need two different behaviors, let's just use another flag (or an
> extra boolean argument if we need to, or something).
Ok, we can pass "bool is_mand" to flock_lock_file that will pass it
further to flock_locks_conflict.
> The only caller for this new deny_lock_file is in the nfs code--I'm a
> little unclear why that is.
deny_lock_file is called not only in the nfs code but also in 2 places
of fs/namei.c -- that enable this logic for VFS.
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