linux-kernel - Re: [PATCH v4 03/11] fs: Initial atomic write support

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Message-Id: <87r0h12080.fsf@doe.com>
Date: Sat, 24 Feb 2024 23:50:15 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: John Garry <john.g.garry@...cle.com>, axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me, jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com, jack@...e.cz
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com, linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com, linux-aio@...ck.org, linux-btrfs@...r.kernel.org, io-uring@...r.kernel.org, nilay@...ux.ibm.com, Prasad Singamsetty <prasad.singamsetty@...cle.com>, John Garry <john.g.garry@...cle.com>
Subject: Re: [PATCH v4 03/11] fs: Initial atomic write support

Ritesh Harjani (IBM) <ritesh.list@...il.com> writes:

> John Garry <john.g.garry@...cle.com> writes:
>
>> From: Prasad Singamsetty <prasad.singamsetty@...cle.com>
>>
>> An atomic write is a write issued with torn-write protection, meaning
>> that for a power failure or any other hardware failure, all or none of the
>> data from the write will be stored, but never a mix of old and new data.
>>
>> Userspace may add flag RWF_ATOMIC to pwritev2() to indicate that the
>> write is to be issued with torn-write prevention, according to special
>> alignment and length rules.
>>
>> For any syscall interface utilizing struct iocb, add IOCB_ATOMIC for
>> iocb->ki_flags field to indicate the same.
>>
>> A call to statx will give the relevant atomic write info for a file:
>> - atomic_write_unit_min
>> - atomic_write_unit_max
>> - atomic_write_segments_max
>>
>> Both min and max values must be a power-of-2.
>>
>> Applications can avail of atomic write feature by ensuring that the total
>> length of a write is a power-of-2 in size and also sized between
>> atomic_write_unit_min and atomic_write_unit_max, inclusive. Applications
>> must ensure that the write is at a naturally-aligned offset in the file
>> wrt the total write length. The value in atomic_write_segments_max
>> indicates the upper limit for IOV_ITER iovcnt.
>>
>> 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.
>>
>> Add a type argument to kiocb_set_rw_flags() to allows reads which have
>> RWF_ATOMIC set to be rejected.
>>
>> Helper function atomic_write_valid() can be used by FSes to verify
>> compliant writes.

Minor nit. 
maybe generic_atomic_write_valid()?