erofs: mark experimental fscache backend deprecated

Although fscache is still described as "General Filesystem Caching" for
network filesystems and other things such as ISO9660 filesystems, it has
actually become a part of netfslib recently, which was unexpected at the
time when "EROFS over fscache" proposed (2021) since EROFS is entirely a
disk filesystem and the dependency is redundant.

Mark it deprecated and it will be removed after "fanotify pre-content
hooks" lands, which will provide the same functionality for EROFS.

Reviewed-by: Sandeep Dhavale <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: hsiangkao

fs/erofs/Kconfig

@@ -145,7 +145,7 @@ config EROFS_FS_ZIP_ZSTD
 	  If unsure, say N.
 
 config EROFS_FS_ONDEMAND
-	bool "EROFS fscache-based on-demand read support"
+	bool "EROFS fscache-based on-demand read support (deprecated)"
 	depends on EROFS_FS
 	select NETFS_SUPPORT
 	select FSCACHE
@@ -155,6 +155,9 @@ config EROFS_FS_ONDEMAND
 	  This permits EROFS to use fscache-backed data blobs with on-demand
 	  read support.
 
+	  It is now deprecated and scheduled to be removed from the kernel
+	  after fanotify pre-content hooks are landed.
+
 	  If unsure, say N.
 
 config EROFS_FS_PCPU_KTHREAD

fs/erofs/super.c

@@ -353,7 +353,7 @@ static int erofs_read_superblock(struct super_block *sb)
 	ret = erofs_scan_devices(sb, dsb);
 
 	if (erofs_is_fscache_mode(sb))
-		erofs_info(sb, "EXPERIMENTAL fscache-based on-demand read feature in use. Use at your own risk!");
+		erofs_info(sb, "[deprecated] fscache-based on-demand read feature in use. Use at your own risk!");
 out:
 	erofs_put_metabuf(&buf);
 	return ret;