ext4: Add feature set check helper for mount & remount paths

A user reported that although his root ext4 filesystem was mounting
fine, other filesystems would not mount, with the:

"Filesystem with huge files cannot be mounted RDWR without CONFIG_LBDAF"

error on his 32-bit box built without CONFIG_LBDAF.  This is because
the test at mount time for this situation was not being re-checked
on remount, and the normal boot process makes an ro->rw transition,
so this was being missed.

Refactor to make a common helper function to test the filesystem
features against the type of mount request (RO vs. RW) so that we
stay consistent.

Addresses Red-Hat-Bugzilla: #517650

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index de67c36..4037fe0 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2254,6 +2254,49 @@ static struct kobj_type ext4_ktype = {
        .release        = ext4_sb_release,
 };
 
+/*
+ * Check whether this filesystem can be mounted based on
+ * the features present and the RDONLY/RDWR mount requested.
+ * Returns 1 if this filesystem can be mounted as requested,
+ * 0 if it cannot be.
+ */
+static int ext4_feature_set_ok(struct super_block *sb, int readonly)
+{
+       if (EXT4_HAS_INCOMPAT_FEATURE(sb, ~EXT4_FEATURE_INCOMPAT_SUPP)) {
+               ext4_msg(sb, KERN_ERR,
+                       "Couldn't mount because of "
+                       "unsupported optional features (%x)",
+                       (le32_to_cpu(EXT4_SB(sb)->s_es->s_feature_incompat) &
+                       ~EXT4_FEATURE_INCOMPAT_SUPP));
+               return 0;
+       }
+
+       if (readonly)
+               return 1;
+
+       /* Check that feature set is OK for a read-write mount */
+       if (EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT4_FEATURE_RO_COMPAT_SUPP)) {
+               ext4_msg(sb, KERN_ERR, "couldn't mount RDWR because of "
+                        "unsupported optional features (%x)",
+                        (le32_to_cpu(EXT4_SB(sb)->s_es->s_feature_ro_compat) &
+                               ~EXT4_FEATURE_RO_COMPAT_SUPP));
+               return 0;
+       }
+       /*
+        * Large file size enabled file system can only be mounted
+        * read-write on 32-bit systems if kernel is built with CONFIG_LBDAF
+        */
+       if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
+               if (sizeof(blkcnt_t) < sizeof(u64)) {
+                       ext4_msg(sb, KERN_ERR, "Filesystem with huge files "
+                                "cannot be mounted RDWR without "
+                                "CONFIG_LBDAF");
+                       return 0;
+               }
+       }
+       return 1;
+}
+
 static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                                __releases(kernel_lock)
                                __acquires(kernel_lock)
@@ -2275,7 +2318,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        unsigned int db_count;
        unsigned int i;
        int needs_recovery, has_huge_files;
-       int features;
        __u64 blocks_count;
        int err;
        unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
@@ -2402,39 +2444,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         * previously didn't change the revision level when setting the flags,
         * so there is a chance incompat flags are set on a rev 0 filesystem.
         */
-       features = EXT4_HAS_INCOMPAT_FEATURE(sb, ~EXT4_FEATURE_INCOMPAT_SUPP);
-       if (features) {
-               ext4_msg(sb, KERN_ERR,
-                       "Couldn't mount because of "
-                       "unsupported optional features (%x)",
-                       (le32_to_cpu(EXT4_SB(sb)->s_es->s_feature_incompat) &
-                       ~EXT4_FEATURE_INCOMPAT_SUPP));
-               goto failed_mount;
-       }
-       features = EXT4_HAS_RO_COMPAT_FEATURE(sb, ~EXT4_FEATURE_RO_COMPAT_SUPP);
-       if (!(sb->s_flags & MS_RDONLY) && features) {
-               ext4_msg(sb, KERN_ERR,
-                       "Couldn't mount RDWR because of "
-                       "unsupported optional features (%x)",
-                       (le32_to_cpu(EXT4_SB(sb)->s_es->s_feature_ro_compat) &
-                       ~EXT4_FEATURE_RO_COMPAT_SUPP));
+       if (!ext4_feature_set_ok(sb, (sb->s_flags & MS_RDONLY)))
                goto failed_mount;
-       }
-       has_huge_files = EXT4_HAS_RO_COMPAT_FEATURE(sb,
-                                   EXT4_FEATURE_RO_COMPAT_HUGE_FILE);
-       if (has_huge_files) {
-               /*
-                * Large file size enabled file system can only be
-                * mount if kernel is build with CONFIG_LBDAF
-                */
-               if (sizeof(root->i_blocks) < sizeof(u64) &&
-                               !(sb->s_flags & MS_RDONLY)) {
-                       ext4_msg(sb, KERN_ERR, "Filesystem with huge "
-                                       "files cannot be mounted read-write "
-                                       "without CONFIG_LBDAF");
-                       goto failed_mount;
-               }
-       }
+
        blocksize = BLOCK_SIZE << le32_to_cpu(es->s_log_block_size);
 
        if (blocksize < EXT4_MIN_BLOCK_SIZE ||
@@ -2470,6 +2482,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                }
        }
 
+       has_huge_files = EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                               EXT4_FEATURE_RO_COMPAT_HUGE_FILE);
        sbi->s_bitmap_maxbytes = ext4_max_bitmap_size(sb->s_blocksize_bits,
                                                      has_huge_files);
        sb->s_maxbytes = ext4_max_size(sb->s_blocksize_bits, has_huge_files);
@@ -3485,18 +3499,11 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
                        if (sbi->s_journal)
                                ext4_mark_recovery_complete(sb, es);
                } else {
-                       int ret;
-                       if ((ret = EXT4_HAS_RO_COMPAT_FEATURE(sb,
-                                       ~EXT4_FEATURE_RO_COMPAT_SUPP))) {
-                               ext4_msg(sb, KERN_WARNING, "couldn't "
-                                      "remount RDWR because of unsupported "
-                                      "optional features (%x)",
-                               (le32_to_cpu(sbi->s_es->s_feature_ro_compat) &
-                                       ~EXT4_FEATURE_RO_COMPAT_SUPP));
+                       /* Make sure we can mount this feature set readwrite */
+                       if (!ext4_feature_set_ok(sb, 0)) {
                                err = -EROFS;
                                goto restore_opts;
                        }
-
                        /*
                         * Make sure the group descriptor checksums
                         * are sane.  If they aren't, refuse to remount r/w.