[PATCH] f2fs: expose resizable_tail feature via sysfs

[Daeho Jeong <daeho43@gmail.com>]

From: Daeho Jeong <daehojeong@google.com>

Userspace has no way to know whether the kernel supports the
resizable_tail_secno mount option before mounting. Passing it to a
kernel without the support fails the mount with -EINVAL, and checking
/sys/fs/f2fs/<disk>/pinned_area_max_secno requires an f2fs instance
to be mounted already.

Export /sys/fs/f2fs/features/resizable_tail so that userspace can check
the support before formatting or mounting a filesystem that relies on
resizable_tail_secno, e.g. a filesystem whose tail is going to be shrunk
online later.

Fixes: c966d29e01bb ("f2fs: support resizable tail section and unify pinned allocation")
Cc: stable@vger.kernel.org
Signed-off-by: Daeho Jeong <daehojeong@google.com>
---
 Documentation/ABI/testing/sysfs-fs-f2fs | 2 +-
 fs/f2fs/sysfs.c                         | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index c4746c416ac..8df18b5d479 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -271,7 +271,7 @@ Description:	Shows all enabled kernel features.
 		inode_crtime, lost_found, verity, sb_checksum,
 		casefold, readonly, compression, test_dummy_encryption_v2,
 		atomic_write, pin_file, encrypted_casefold, linear_lookup,
-		fserror.
+		fserror, resizable_tail.
 
 What:		/sys/fs/f2fs/<disk>/inject_rate
 Date:		May 2016
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 9749da70089..8b844a8b0bf 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -1421,6 +1421,7 @@ F2FS_FEATURE_RO_ATTR(linear_lookup);
 #endif
 F2FS_FEATURE_RO_ATTR(packed_ssa);
 F2FS_FEATURE_RO_ATTR(fserror);
+F2FS_FEATURE_RO_ATTR(resizable_tail);
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
@@ -1592,6 +1593,7 @@ static struct attribute *f2fs_feat_attrs[] = {
 #endif
 	BASE_ATTR_LIST(packed_ssa),
 	BASE_ATTR_LIST(fserror),
+	BASE_ATTR_LIST(resizable_tail),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs_feat);
-- 
2.56.0.385.gd3acb90ef8-goog