linux-ext4 - [PATCH V2] ext4: don't complain about incorrect features when probing

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Message-ID: <e5c4f332-a61a-372a-5396-0ce05f258967@redhat.com>
Date:   Fri, 2 Mar 2018 10:51:28 -0600
From:   Eric Sandeen <sandeen@...hat.com>
To:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Cc:     Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
Subject: [PATCH V2] ext4: don't complain about incorrect features when probing

If mount is auto-probing for filesystem type, it will try various
filesystems in order, with the MS_SILENT flag set.  We get
that flag as the silent arg to ext4_fill_super.

If we're probing (silent==1) then don't complain about feature
incompatibilities that are found if it looks like it's actually
a different valid extN type - failed probes should be silent
in this case.

If the on-disk features are unknown even to ext4, then complain.

Reported-by: Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---

compile-tested only, sorry.

V2.  I lied.  (actually I hand-edited the patch in mail)  /Now/ it's compile tested,
with the proper args to ext4_feature_set_ok :/

Having 2 gotos like this might not be preferable, but trying
to write it more compactly led to what I thought was more
difficult-to-read logic.

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b0915b7..ae40368 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3659,6 +3659,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			ext4_msg(sb, KERN_INFO, "mounting ext2 file system "
 				 "using the ext4 subsystem");
 		else {
+			/*
+			 * If we're probing be silent, if this looks like
+			 * it's actually an ext[34] filesystem.
+			 */
+			if (silent && ext4_feature_set_ok(sb, sb_rdonly(sb)))
+				goto failed_mount;
 			ext4_msg(sb, KERN_ERR, "couldn't mount as ext2 due "
 				 "to feature incompatibilities");
 			goto failed_mount;
@@ -3670,6 +3676,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			ext4_msg(sb, KERN_INFO, "mounting ext3 file system "
 				 "using the ext4 subsystem");
 		else {
+			/*
+			 * If we're probing be silent, if this looks like
+			 * it's actually an ext4 filesystem.
+			 */
+			if (silent && ext4_feature_set_ok(sb, sb_rdonly(sb)))
+				goto failed_mount;
 			ext4_msg(sb, KERN_ERR, "couldn't mount as ext3 due "
 				 "to feature incompatibilities");
 			goto failed_mount;