[PATCH v2] erofs: Fallback to normal access if DAX is not supported on extra device

Yuezhang.Mo at sony.com Yuezhang.Mo at sony.com
Wed Jul 30 19:24:04 AEST 2025


On 2025/7/29 11:07, Hongbo Li wrote:
> On 2025/7/28 12:54, 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>
> > ---
> >   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..b08016bf9d1e 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) {
> > +           errorfc(fc, "unsupported blocksize for DAX");
>
> How about using the info log? Can we consider using infofc in this case?
>

This is not a case of error, I also think using the info log is better.

In erofs_init_device() and erofs_scan_devices(), use erofs_info() to output the
logs of turning off DAX. How about using erofs_info() uniformly?


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