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

[Giuseppe Scrivano <gscrivan@redhat.com>]

Gao Xiang <hsiangkao@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 <gscrivan@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)