[PATCH v2 0/8] Add O_DENY* support for VFS and CIFS/NFS

[Pavel Shilovsky]

2013/1/18 Stephen Rothwell <sfr at canb.auug.org.au>:
> Hi Pavel,
>
> On Thu, 17 Jan 2013 20:52:09 +0400 Pavel Shilovsky <piastry at etersoft.ru> wrote:
>>
>> This patchset adds support of O_DENY* flags for Linux fs layer. These flags can be used by any application that needs share reservations to organize a file access. VFS already has some sort of this capability - now it's done through flock/LOCK_MAND mechanis, but that approach is non-atomic. This patchset build new capabilities on top of the existing one but doesn't bring any changes into the flock call semantic.
>
> This has probably been discussed, but is Linux's leases implementation
> not sufficient?  Just wondering.

As I understand it, leases play different role: they allow to cache a
data for the particular open and then flush it when a lease break
comes. But we need to protect opens from being done if their
access/share mode is not suitable for previously done opens. E.g. if
we have already opened a file with O_RDONLY | O_DENYWRITE we can't
open it again with any of O_WRONLY, O_RDWR and O_DENYREAD flags (of
course all these things should only work if O_DENYMAND is specified
for the first and the second opens).

-- 
Best regards,
Pavel Shilovsky.