[LTP] [PATCH v2 2/2] aio_tio: determine alignment based on target filesystem

Matthias Männich maennich@google.com
Tue Feb 26 16:37:00 CET 2019


On 22/02/2019 15:33, Cyril Hrubis wrote:
>> The alignment for O_DIRECT operations has to match the blocksize of the
>> underlying filesystem. Determine the alignment from the target file's
>> file system.
>> aio_tio test cases 1 and 2 failed (nondeterministic) on aarch64 when run
>> on a 4096 byte blocksize filesystem and with an alignment of 512 bytes.
> Is this really about the filesystem? Citing man open:
>         Under Linux 2.4, transfer sizes, and the alignment of the  user  buffer
>         and  the file offset must all be multiples of the logical block size of
>         the filesystem.  Since Linux 2.6.0, alignment to the logical block size
>         of  the underlying storage (typically 512 bytes) suffices.  The logical
>         block size can be determined using the ioctl(2) BLKSSZGET operation  or
>         from the shell using the command:
>         blockdev --getss
> So unless you are running ancient 2.4 kernel the aligment restrictions should
> be result of the blocksize of the device rather than of the filesystem.

Yes. You are right. The blocksize of the device is what I was referring 
to. Sorry for that.
In particular the test hits the alignment check in fs/direct-io.c 
(do_blockdev_direct_IO) [1], which makes the direct io operation fail in 
my case with EINVAL.

> What does the blockdev command return on the particular system?

I will update the patch to correct comment and commit message.


[1] https://elixir.bootlin.com/linux/v4.20/source/fs/direct-io.c#L1199

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