ext4l: Update symlink to replace existing files

The ext4l_ln() function returned -EEXIST when creating a symlink where
a file already exists. This differs from the old ext4 implementation
which deletes any existing file before creating the symlink (like ln -sf
behaviour).

Update ext4l_ln() to match this behaviour by calling __ext4_unlink() to
remove any existing non-directory file before creating the symlink.
Directories cannot be replaced with symlinks and return -EISDIR.

This allows test_symlink3 to pass.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

fs/ext4l/interface.c

@@ -1268,9 +1268,21 @@ int ext4l_ln(const char *filename, const char *linkname)
 		return ret;
 
 	if (dentry->d_inode) {
-		/* File already exists */
-		ret = -EEXIST;
-		goto out;
+		/* File already exists - delete it first (like ln -sf) */
+		if (S_ISDIR(dentry->d_inode->i_mode)) {
+			/* Cannot replace a directory with a symlink */
+			ret = -EISDIR;
+			goto out;
+		}
+
+		ret = __ext4_unlink(dir_dentry->d_inode, &dentry->d_name,
+				    dentry->d_inode, dentry);
+		if (ret)
+			goto out;
+
+		/* Release inode to free data blocks */
+		iput(dentry->d_inode);
+		dentry->d_inode = NULL;
 	}
 
 	/* Create the symlink - filename is what the link points to */

include/ext4l.h

@@ -114,9 +114,12 @@ int ext4l_mkdir(const char *dirname);
 /**
  * ext4l_ln() - Create a symbolic link
  *
+ * Creates the symlink, replacing any existing file (like ln -sf).
+ * Refuses to replace a directory.
+ *
  * @filename: Path of symlink to create
  * @target: Target path the symlink points to
- * Return: 0 on success, -EEXIST if file already exists,
+ * Return: 0 on success, -EISDIR if target is a directory,
  *	   -ENOTDIR if parent is not a directory, -EROFS if read-only,
  *	   negative on other errors
  */

test/fs/ext4l.c

@@ -576,8 +576,8 @@ static int fs_test_ext4l_ln_norun(struct unit_test_state *uts)
 	ut_asserteq(12, actread);
 	ut_asserteq_str("hello world\n", buf);
 
-	/* Verify creating duplicate returns -EEXIST */
-	ut_asserteq(-EEXIST, ext4l_ln(target, link_name));
+	/* Verify creating duplicate succeeds (like ln -sf) */
+	ut_assertok(ext4l_ln(target, link_name));
 
 	/* Verify creating symlink in non-existent parent returns -ENOENT */
 	ut_asserteq(-ENOENT, ext4l_ln(target, "/nonexistent/link"));