EXTLINUX: Add sanity check for XFS filesystems

Syslinux won't work on >4 KiB filesystem block sizes since there is no
left space in MBR to determine where to install Syslinux bootsector.

If one is trying to install Syslinux in a XFS partition with a
filesystem block size different of 4 KiB, a proper error will be
returned to the user informing that the current filesystem block size
isn't supported by Syslinux.

Reported-by: Gene Cumm <gene.cumm@gmail.com>
Signed-off-by: Paulo Alcantara <pcacjr@zytor.com>

2 files changed, 67 insertions, 3 deletions

diff --git a/extlinux/main.c b/extlinux/main.c
index bbcc8db3..d1a800cd 100644
--- a/extlinux/main.c
+++ b/extlinux/main.c
@@ -14,7 +14,8 @@
 /*
  * extlinux.c
  *
- * Install the syslinux boot block on an fat, ntfs, ext2/3/4 and btrfs filesystem
+ * Install the syslinux boot block on an fat, ntfs, ext2/3/4, btrfs and xfs
+ * filesystem.
  */
 
 #define  _GNU_SOURCE		/* Enable everything */
@@ -49,6 +50,7 @@
 #include "xfs.h"
 #include "xfs_types.h"
 #include "xfs_sb.h"
+#include "misc.h"
 #include "../version.h"
 #include "syslxint.h"
 #include "syslxcom.h" /* common functions shared with extlinux and syslinux */
@@ -71,7 +73,8 @@
  * we will use the first 0~512 bytes starting from 2048 for the Syslinux
  * boot sector.
  */
-#define XFS_BOOTSECT_OFFSET	4 * SECTOR_SIZE
+#define XFS_BOOTSECT_OFFSET	(4 << SECTOR_SHIFT)
+#define XFS_SUPPORTED_BLOCKSIZE 4096 /* 4 KiB filesystem block size */
 
 /* the btrfs partition first 64K blank area is used to store boot sector and
    boot image, the boot sector is from 0~512, the boot image starts after */
@@ -379,8 +382,19 @@ int install_bootblock(int fd, const char *device)
 	    return 1;
 	}
 
-	if (sb5.sb_magicnum == *(u32 *)XFS_SB_MAGIC)
+	if (sb5.sb_magicnum == *(u32 *)XFS_SB_MAGIC) {
+	    if (be32_to_cpu(sb5.sb_blocksize) != XFS_SUPPORTED_BLOCKSIZE) {
+		fprintf(stderr,
+			"You need to have 4 KiB filesystem block size for "
+			" being able to install Syslinux in your XFS "
+			"partition (because there is no enough space in MBR to "
+			"determine where Syslinux bootsector can be installed "
+			"regardless the filesystem block size)\n");
+		return 1;
+	    }
+
 	    ok = true;
+	}
     }
 
     if (!ok) {
diff --git a/extlinux/misc.h b/extlinux/misc.h
new file mode 100644
index 00000000..7f2f1b33
--- /dev/null
+++ b/extlinux/misc.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2012 Paulo Alcantara <pcacjr@zytor.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#ifndef MISC_H_
+#define MISC_H_
+
+/* Return a 64-bit litte-endian value from a given 64-bit big-endian one */
+static inline uint64_t be64_to_cpu(uint64_t val)
+{
+    return (uint64_t)((((uint64_t)val & (uint64_t)0x00000000000000ffULL) << 56) |
+		      (((uint64_t)val & (uint64_t)0x000000000000ff00ULL) << 40) |
+		      (((uint64_t)val & (uint64_t)0x0000000000ff0000ULL) << 24) |
+		      (((uint64_t)val & (uint64_t)0x00000000ff000000ULL) <<  8) |
+		      (((uint64_t)val & (uint64_t)0x000000ff00000000ULL) >>  8) |
+		      (((uint64_t)val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
+		      (((uint64_t)val & (uint64_t)0x00ff000000000000ULL) >> 40) |
+		      (((uint64_t)val & (uint64_t)0xff00000000000000ULL) >> 56));
+}
+
+/* Return a 32-bit litte-endian value from a given 32-bit big-endian one */
+static inline uint32_t be32_to_cpu(uint32_t val)
+{
+    return (uint32_t)((((uint32_t)val & (uint32_t)0x000000ffUL) << 24) |
+		      (((uint32_t)val & (uint32_t)0x0000ff00UL) <<  8) |
+		      (((uint32_t)val & (uint32_t)0x00ff0000UL) >>  8) |
+		      (((uint32_t)val & (uint32_t)0xff000000UL) >> 24));
+}
+
+/* Return a 16-bit litte-endian value from a given 16-bit big-endian one */
+static inline uint16_t be16_to_cpu(uint16_t val)
+{
+    return (uint16_t)((((uint16_t)val & (uint16_t)0x00ffU) << 8) |
+		      (((uint16_t)val & (uint16_t)0xff00U) >> 8));
+}
+
+#endif /* MISC_H_ */