[PATCH v3] erofs: Fallback to normal access if DAX is not supported on extra device
Hongbo Li
lihongbo22 at huawei.com
Mon Aug 4 21:04:50 AEST 2025
On 2025/8/4 16:20, Yuezhang Mo wrote:
> If using multiple devices, we should check if the extra device support
> DAX instead of checking the primary device when deciding if to use DAX
> to access a file.
>
> If an extra device does not support DAX we should fallback to normal
> access otherwise the data on that device will be inaccessible.
>
> Signed-off-by: Yuezhang Mo <Yuezhang.Mo at sony.com>
> Reviewed-by: Friendy Su <friendy.su at sony.com>
> Reviewed-by: Jacky Cao <jacky.cao at sony.com>
> Reviewed-by: Daniel Palmer <daniel.palmer at sony.com>
Reviewed-by: Hongbo Li <lihongbo22 at huawei.com>
Thanks,
Hongbo
> ---
>
> Changes of v3:
> - uniformly use erofs_info() to output the logs of turning off DAX
>
> Changes of v2:
> - fix the indentation alignment of `dif->path`
> - remove the unnecessary comment
>
> fs/erofs/super.c | 24 ++++++++++++++----------
> 1 file changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index e1020aa60771..8c7a5985b4ee 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -174,6 +174,11 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
> if (!erofs_is_fileio_mode(sbi)) {
> dif->dax_dev = fs_dax_get_by_bdev(file_bdev(file),
> &dif->dax_part_off, NULL, NULL);
> + if (!dif->dax_dev && test_opt(&sbi->opt, DAX_ALWAYS)) {
> + erofs_info(sb, "DAX unsupported by %s. Turning off DAX.",
> + dif->path);
> + clear_opt(&sbi->opt, DAX_ALWAYS);
> + }
> } else if (!S_ISREG(file_inode(file)->i_mode)) {
> fput(file);
> return -EINVAL;
> @@ -210,8 +215,13 @@ static int erofs_scan_devices(struct super_block *sb,
> ondisk_extradevs, sbi->devs->extra_devices);
> return -EINVAL;
> }
> - if (!ondisk_extradevs)
> + if (!ondisk_extradevs) {
> + if (test_opt(&sbi->opt, DAX_ALWAYS) && !sbi->dif0.dax_dev) {
> + erofs_info(sb, "DAX unsupported by block device. Turning off DAX.");
> + clear_opt(&sbi->opt, DAX_ALWAYS);
> + }
> return 0;
> + }
>
> if (!sbi->devs->extra_devices && !erofs_is_fscache_mode(sb))
> sbi->devs->flatdev = true;
> @@ -338,7 +348,6 @@ static int erofs_read_superblock(struct super_block *sb)
> if (ret < 0)
> goto out;
>
> - /* handle multiple devices */
> ret = erofs_scan_devices(sb, dsb);
>
> if (erofs_sb_has_48bit(sbi))
> @@ -671,14 +680,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
> return invalfc(fc, "cannot use fsoffset in fscache mode");
> }
>
> - if (test_opt(&sbi->opt, DAX_ALWAYS)) {
> - if (!sbi->dif0.dax_dev) {
> - errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
> - clear_opt(&sbi->opt, DAX_ALWAYS);
> - } else if (sbi->blkszbits != PAGE_SHIFT) {
> - errorfc(fc, "unsupported blocksize for DAX");
> - clear_opt(&sbi->opt, DAX_ALWAYS);
> - }
> + if (test_opt(&sbi->opt, DAX_ALWAYS) && sbi->blkszbits != PAGE_SHIFT) {
> + erofs_info(sb, "unsupported blocksize for DAX");
> + clear_opt(&sbi->opt, DAX_ALWAYS);
> }
>
> sb->s_time_gran = 1;
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