Re: [PATCH v3] erofs: accept source file descriptor via fsconfig

[Giuseppe Scrivano]

Gao Xiang <hsiang...@linux.alibaba.com> writes:

> Hi Giuseppe,
>
> On 2026/7/14 23:48, Giuseppe Scrivano wrote:
>> Allow userspace to pass an already-opened file descriptor as the mount
>> source instead of a path string.  This is useful for tools that already
>> hold an fd to the image, such as composefs reusing an existing erofs
>> backing file.
>> Signed-off-by: Giuseppe Scrivano <gscri...@redhat.com>
>
> Use the current erofs-utils testsuite, the following tests seems skipped 
> incorrectly.
>
> [Error 22] Invalid argument
> SKIP: erofs/008
> [Error 22] Invalid argument
> SKIP: erofs/009
> [Error 22] Invalid argument
> SKIP: erofs/010
> [Error 22] Invalid argument
> SKIP: erofs/011
>
> [Error 22] Invalid argument
> SKIP: erofs/017
> [Error 22] Invalid argument
> SKIP: erofs/018
>
> And the kernel message shows:
> [  116.477816] erofs: source is unsupported
> ...
>
> git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git -b 
> experimental-tests
> $ sudo make check
>
> Thanks,
> Gao Xiang

it seems to be caused by the different error returned by erofs_fc_get_tree.

Would you be fine if I amend this on top of v3?

Thanks,
Giuseppe



diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index d7baf9f34dc0..829ae530d7ca 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -791,17 +791,22 @@ static int erofs_fc_fill_super(struct super_block *sb, 
struct fs_context *fc)
 static int erofs_fc_get_tree(struct fs_context *fc)
 {
        struct erofs_sb_info *sbi = fc->s_fs_info;
-       struct file *file = sbi->dif0.file;
+       int ret;
 
-       if (!IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) || !file) {
-               int ret;
+       if (IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && sbi->dif0.file) {
+               if (!S_ISREG(file_inode(sbi->dif0.file)->i_mode) ||
+                   !sbi->dif0.file->f_mapping->a_ops->read_folio) {
+                       errorfc(fc, "source is unsupported");
+                       return -EINVAL;
+               }
+               return get_tree_nodev(fc, erofs_fc_fill_super);
+       }
 
-               ret = get_tree_bdev_flags(fc, erofs_fc_fill_super,
-                       IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ?
-                               GET_TREE_BDEV_QUIET_LOOKUP : 0);
-               if (!IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ||
-                   ret != -ENOTBLK)
-                       return ret;
+       ret = get_tree_bdev_flags(fc, erofs_fc_fill_super,
+               IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ?
+                       GET_TREE_BDEV_QUIET_LOOKUP : 0);
+       if (IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && ret == -ENOTBLK) {
+               struct file *file;
 
                if (!fc->source)
                        return invalf(fc, "No source specified");
@@ -809,13 +814,12 @@ static int erofs_fc_get_tree(struct fs_context *fc)
                if (IS_ERR(file))
                        return PTR_ERR(file);
                sbi->dif0.file = file;
+
+               if (S_ISREG(file_inode(sbi->dif0.file)->i_mode) &&
+                   sbi->dif0.file->f_mapping->a_ops->read_folio)
+                       return get_tree_nodev(fc, erofs_fc_fill_super);
        }
-       if (!S_ISREG(file_inode(file)->i_mode) ||
-           !file->f_mapping->a_ops->read_folio) {
-               errorfc(fc, "source is unsupported");
-               return -EINVAL;
-       }
-       return get_tree_nodev(fc, erofs_fc_fill_super);
+       return ret;
 }
 
 static int erofs_fc_reconfigure(struct fs_context *fc)