Re: [PATCH] resctrl: Do not open directory for writing
On 7/10/20 3:39 PM, Andrea Bolognani wrote:
On Fri, 2020-07-10 at 15:13 +0200, Martin Kletzander wrote:
> On Fri, Jul 10, 2020 at 10:47:22AM +0200, Michal Privoznik wrote:
>> On 7/9/20 6:30 PM, Andrea Bolognani wrote:
>>> This is all bikeshedding, of course: what actually matters is making
>>> that lock exclusive once again :)
>>
>> Just realized that for exclusive (aka write) lock, the FD must be opened
>> for writing (working on patches for the following report [1] and been
>> experimenting a bit and that's what I'm seeing).
>
> Good point, but luckily not related to flock(2).
That seems to be the case: according to flock(2),
A shared or exclusive lock can be placed on a file regardless
of the mode in which the file was opened.
Michal, does that sound reasonable to you?
D'oh! of course this is another case of file locking exemptions. The
patches I sent earlier today fix code around virFileLock() which is
fcntl() which is POSIX locking. flock(2) is BSD lock which may or may
not be implementedusing POSIX locks.
So I think we're okay on that front.
Alternatively, we may switch to OFD (F_OFD_SETLK from fcntl(2)) and
experience proper file locking. Those are Linux only (but so is resctrl).
Michal