linux-kernel - Re: [PATCH v2 05/16] fs: Add RWF_ATOMIC and IOCB

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Date:   Wed, 13 Dec 2023 16:02:35 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        brauner@...nel.org, dchinner@...hat.com, jack@...e.cz,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-scsi@...r.kernel.org, ming.lei@...hat.com,
        jaswin@...ux.ibm.com, bvanassche@....org,
        Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH v2 05/16] fs: Add RWF_ATOMIC and IOCB_ATOMIC flags for
 atomic write support

On 13/12/2023 13:31, Al Viro wrote:
>> Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
>> flag set will have RWF_ATOMIC rejected and not just ignored.
>>
>> Signed-off-by: Prasad Singamsetty<prasad.singamsetty@...cle.com>
>> Signed-off-by: John Garry<john.g.garry@...cle.com>
>> ---
>>   include/linux/fs.h      | 8 ++++++++
>>   include/uapi/linux/fs.h | 5 ++++-
>>   2 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 70329c81be31..d725c194243c 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -185,6 +185,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>>   /* File supports async nowait buffered writes */
>>   #define FMODE_BUF_WASYNC	((__force fmode_t)0x80000000)
>>   
>> +/* File supports atomic writes */
>> +#define FMODE_CAN_ATOMIC_WRITE	((__force fmode_t)0x100000000)
> Have you even tried to compile that on e.g. arm?

i386 and now arm32, and no grumblings.

I think that the issue is that we only ever do a bitwise OR or test that 
bit 33 for a 32b value, and it is a void operation and ignored.

However if I have file.f_mode = FMODE_CAN_ATOMIC_WRITE and compile for 
arm32, then it complains.