Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

Bart Van Assche
2023-10-01T13:23:38Z

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.
>
>> +#define STATX_ATTR_WRITE_ATOMIC 0x00400000 /* File supports atomic write operations */
>
> How would this differ from 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.

Thanks,

Bart.