blkid: Add fallback to ext4 for 2.6.29+ kernels if ext2 is not present

Starting in 2.6.29, ext4 can be used to support filesystems without a
journal.  So if ext2 is not present, and the kernel version is greater
than 2.6.29, and ext4 is present, return a filesystme type of ext4.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/blkid/probe.c b/lib/blkid/probe.c
index ea57598..b90c7eb 100644 (file)
--- a/lib/blkid/probe.c
+++ b/lib/blkid/probe.c
@@ -245,6 +245,55 @@ static int check_for_modules(const char *fs_name)
        return (0);
 }
 
+static int linux_version_code()
+{
+#ifdef __linux__
+       struct utsname  ut;
+       static          version_code = -1;
+       int             major, minor, rev;
+       char            *endptr;
+       const char      *cp;
+
+       if (version_code > 0)
+               return version_code;
+
+       if (uname(&ut))
+               return 0;
+       cp = ut.release;
+
+       major = strtol(cp, &endptr, 10);
+       if (cp == endptr || *endptr != '.')
+               return 0;
+       cp = endptr + 1;
+       minor = strtol(cp, &endptr, 10);
+       if (cp == endptr || *endptr != '.')
+               return 0;
+       cp = endptr + 1;
+       rev = strtol(cp, &endptr, 10);
+       if (cp == endptr)
+               return 0;
+       version_code = (((major * 256) + minor) * 256) + rev;
+       return version_code;
+#else
+       return 0;
+#endif
+}
+
+#define EXT4_SUPPORTS_EXT2 (2 * 65536 + 6*256 + 29)
+
+static int system_supports_ext2(void)
+{
+       static time_t   last_check = 0;
+       static int      ret = -1;
+       time_t          now = time(0);
+
+       if (ret != -1 || (now - last_check) < 5)
+               return ret;
+       last_check = now;
+       ret = (fs_proc_check("ext2") || check_for_modules("ext2"));
+       return ret;
+}
+
 static int system_supports_ext4(void)
 {
        static time_t   last_check = 0;
@@ -283,6 +332,18 @@ static int probe_ext4dev(struct blkid_probe *probe,
            EXT3_FEATURE_INCOMPAT_JOURNAL_DEV)
                return -BLKID_ERR_PARAM;
 
+       /* 
+        * If the filesystem does not have a journal and ext2 and ext4
+        * is not present, then force this to be detected as an
+        * ext4dev filesystem.
+        */
+       if (!(blkid_le32(es->s_feature_compat) &
+             EXT3_FEATURE_COMPAT_HAS_JOURNAL) &&
+           !system_supports_ext2() && !system_supports_ext4() &&
+           system_supports_ext4dev() &&
+           linux_version_code() >= EXT4_SUPPORTS_EXT2)
+               goto force_ext4dev;
+
        /*
         * If the filesystem is marked as OK for use by in-development
         * filesystem code, but ext4dev is not supported, and ext4 is,
@@ -299,6 +360,7 @@ static int probe_ext4dev(struct blkid_probe *probe,
        } else
                return -BLKID_ERR_PARAM;
 
+force_ext4dev:
        get_ext2_info(probe->dev, id, buf);
        return 0;
 }
@@ -314,6 +376,17 @@ static int probe_ext4(struct blkid_probe *probe, struct blkid_magic *id,
            EXT3_FEATURE_INCOMPAT_JOURNAL_DEV)
                return -BLKID_ERR_PARAM;
 
+       /* 
+        * If the filesystem does not have a journal and ext2 is not
+        * present, then force this to be detected as an ext2
+        * filesystem.
+        */
+       if (!(blkid_le32(es->s_feature_compat) &
+             EXT3_FEATURE_COMPAT_HAS_JOURNAL) &&
+           !system_supports_ext2() && system_supports_ext4() &&
+           linux_version_code() >= EXT4_SUPPORTS_EXT2)
+               goto force_ext4;
+
        /* Ext4 has at least one feature which ext3 doesn't understand */
        if (!(blkid_le32(es->s_feature_ro_compat) &
              EXT3_FEATURE_RO_COMPAT_UNSUPPORTED) &&
@@ -321,6 +394,7 @@ static int probe_ext4(struct blkid_probe *probe, struct blkid_magic *id,
              EXT3_FEATURE_INCOMPAT_UNSUPPORTED))
                return -BLKID_ERR_PARAM;
 
+force_ext4:
        /*
         * If the filesystem is a OK for use by in-development
         * filesystem code, and ext4dev is supported or ext4 is not
@@ -380,6 +454,15 @@ static int probe_ext2(struct blkid_probe *probe, struct blkid_magic *id,
             EXT2_FEATURE_INCOMPAT_UNSUPPORTED))
                return -BLKID_ERR_PARAM;
 
+       /* 
+        * If ext2 is not present, but ext4 or ext4dev are, then
+        * disclaim we are ext2
+        */
+       if (!system_supports_ext2() &&
+           (system_supports_ext4() || system_supports_ext4dev()) &&
+           linux_version_code() >= EXT4_SUPPORTS_EXT2)
+               return -BLKID_ERR_PARAM;
+
        get_ext2_info(probe->dev, id, buf);
        return 0;
 }