Andreas,
What about to disable a O_DIRECT global on any block devices in the e2fsprogs library as this don’t work on 4k disk drives at all ?
Instead of fixing an O_DIRECT access with patches sends early.
Alex
> 19 февр. 2021 г., в 1:20, Andreas Dilger <adilger@xxxxxxxxx> написал(а):
>
> On Feb 18, 2021, at 2:51 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
>>
>> Currently the mmp block is read using O_DIRECT to avoid any caching that
>> may be done by the VM. However when working with regular files this
>> creates alignment issues when the device of the host file system has
>> sector size larger than the blocksize of the file system in the file
>> we're working with.
>>
>> This can be reproduced with t_mmp_fail test when run on the device with
>> 4k sector size because the mke2fs fails when trying to read the mmp
>> block.
>>
>> Fix it by disabling O_DIRECT when working with regular files. I don't
>> think there is any risk of doing so since the file system layer, unlike
>> shared block device, should guarantee cache consistency.
>>
>> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
>> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>
> Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
>
>> ---
>> v2: Fix comment - it avoids problems when the sector size is larger not
>> smaller than blocksize
>>
>> lib/ext2fs/mmp.c | 22 +++++++++++-----------
>> 1 file changed, 11 insertions(+), 11 deletions(-)
>>
>> diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
>> index c21ae272..cca2873b 100644
>> --- a/lib/ext2fs/mmp.c
>> +++ b/lib/ext2fs/mmp.c
>> @@ -57,21 +57,21 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
>> * regardless of how the io_manager is doing reads, to avoid caching of
>> * the MMP block by the io_manager or the VM. It needs to be fresh. */
>> if (fs->mmp_fd <= 0) {
>> + struct stat st;
>> int flags = O_RDWR | O_DIRECT;
>>
>> -retry:
>> + /*
>> + * There is no reason for using O_DIRECT if we're working with
>> + * regular file. Disabling it also avoids problems with
>> + * alignment when the device of the host file system has sector
>> + * size larger than blocksize of the fs we're working with.
>> + */
>> + if (stat(fs->device_name, &st) == 0 &&
>> + S_ISREG(st.st_mode))
>> + flags &= ~O_DIRECT;
>> +
>> fs->mmp_fd = open(fs->device_name, flags);
>> if (fs->mmp_fd < 0) {
>> - struct stat st;
>> -
>> - /* Avoid O_DIRECT for filesystem image files if open
>> - * fails, since it breaks when running on tmpfs. */
>> - if (errno == EINVAL && (flags & O_DIRECT) &&
>> - stat(fs->device_name, &st) == 0 &&
>> - S_ISREG(st.st_mode)) {
>> - flags &= ~O_DIRECT;
>> - goto retry;
>> - }
>> retval = EXT2_ET_MMP_OPEN_DIRECT;
>> goto out;
>> }
>> --
>> 2.26.2
>>
>
>
> Cheers, Andreas
>
>
>
>
>
