Re: [PATCH v3] erofs: Fallback to normal access if DAX is not supported on extra device

[Hongbo Li]

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...@sony.com>
Reviewed-by: Friendy Su <friendy...@sony.com>
Reviewed-by: Jacky Cao <jacky....@sony.com>
Reviewed-by: Daniel Palmer <daniel.pal...@sony.com>

Reviewed-by: Hongbo Li <lihongb...@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;