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Message-ID: <d3a8b9b0-b24c-a002-e77d-56380ee785a5@oracle.com>
Date: Mon, 2 Oct 2023 10:51:36 +0100
From: John Garry <john.g.garry@...cle.com>
To: Bart Van Assche <bvanassche@....org>,
Eric Biggers <ebiggers@...nel.org>
Cc: 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,
chandan.babu@...cle.com, dchinner@...hat.com,
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-api@...r.kernel.org,
Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx
On 01/10/2023 14:23, Bart Van Assche wrote:
> On 9/29/23 15:49, Eric Biggers wrote:
>> On Fri, Sep 29, 2023 at 10:27:08AM +0000, John Garry wrote:
>>> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
>>> index 7cab2c65d3d7..c99d7cac2aa6 100644
>>> --- a/include/uapi/linux/stat.h
>>> +++ b/include/uapi/linux/stat.h
>>> @@ -127,7 +127,10 @@ struct statx {
>>> __u32 stx_dio_mem_align; /* Memory buffer alignment for
>>> direct I/O */
>>> __u32 stx_dio_offset_align; /* File offset alignment for
>>> direct I/O */
>>> /* 0xa0 */
>>> - __u64 __spare3[12]; /* Spare space for future expansion */
>>> + __u32 stx_atomic_write_unit_max;
>>> + __u32 stx_atomic_write_unit_min;
>>
>> Maybe min first and then max? That seems a bit more natural, and a
>> lot of the
>> code you've written handle them in that order.
ok, I think it's fine to reorder
>>
>>> +#define STATX_ATTR_WRITE_ATOMIC 0x00400000 /* File supports
>>> atomic write operations */
>>
>> How would this differ from stx_atomic_write_unit_min != 0?
Yeah, I suppose that we can just not set this for the case of
stx_atomic_write_unit_min == 0.
>
> Is it even possible that stx_atomic_write_unit_min == 0? My understanding
> is that all Linux filesystems rely on the assumption that writing a single
> logical block either succeeds or does not happen, even if a power failure
> occurs between writing and reading a logical block.
>
Maybe they do rely on this, but is it particularly interesting?
BTW, I would not like to provide assurances that every storage media
produced writes logical blocks atomically.
Thanks,
John
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