Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk addressability check

[Joel Becker <Joel.Becker@oracle.com>]

On Thu, Aug 12, 2010 at 03:32:27PM -0600, Andreas Dilger wrote:
> > 	If I change the BUG_ON()s to -EINVAL, does that work?  Or do you
> > have some way you'd like to allow non-pagecache filesystems to use this
> > as well?
> 
> That's probably fine for now.  If anyone complains, we can always change it later, since they can't possibly depend on this function yet...

	How's this:

>From f988b04c58039ae9a65fea537656088ea56a8072 Mon Sep 17 00:00:00 2001
>From: Patrick J. LoPresti <lopresti@gmail.com>
Date: Thu, 22 Jul 2010 15:03:41 -0700
Subject: [PATCH] ext3/ext4: Factor out disk addressability check

As part of adding support for OCFS2 to mount huge volumes, we need to
check that the sector_t and page cache of the system are capable of
addressing the entire volume.

An identical check already appears in ext3 and ext4.  This patch moves
the addressability check into its own function in fs/libfs.c and
modifies ext3 and ext4 to invoke it.

[Edited to -EINVAL instead of BUG_ON() for bad blocksize_bits -- Joel]

Signed-off-by: Patrick LoPresti <lopresti@gmail.com>
Cc: linux-ext4@vger.kernel.org
Signed-off-by: Joel Becker <joel.becker@oracle.com>
---
 fs/ext3/super.c    |    4 ++--
 fs/ext4/super.c    |    8 +++-----
 fs/libfs.c         |   29 +++++++++++++++++++++++++++++
 include/linux/fs.h |    2 ++
 4 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 6c953bb..d0643db 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -1862,8 +1862,8 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
 		goto failed_mount;
 	}
 
-	if (le32_to_cpu(es->s_blocks_count) >
-		    (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
+	if (generic_check_addressable(sb->s_blocksize_bits,
+				      le32_to_cpu(es->s_blocks_count))) {
 		ext3_msg(sb, KERN_ERR,
 			"error: filesystem is too large to mount safely");
 		if (sizeof(sector_t) < 8)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e72d323..e03a7d2 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2706,15 +2706,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	 * Test whether we have more sectors than will fit in sector_t,
 	 * and whether the max offset is addressable by the page cache.
 	 */
-	if ((ext4_blocks_count(es) >
-	     (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) ||
-	    (ext4_blocks_count(es) >
-	     (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - sb->s_blocksize_bits))) {
+	ret = generic_check_addressable(sb->s_blocksize_bits,
+					ext4_blocks_count(es));
+	if (ret) {
 		ext4_msg(sb, KERN_ERR, "filesystem"
 			 " too large to mount safely on this system");
 		if (sizeof(sector_t) < 8)
 			ext4_msg(sb, KERN_WARNING, "CONFIG_LBDAF not enabled");
-		ret = -EFBIG;
 		goto failed_mount;
 	}
 
diff --git a/fs/libfs.c b/fs/libfs.c
index dcaf972..f099566 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -955,6 +955,35 @@ int generic_file_fsync(struct file *file, int datasync)
 }
 EXPORT_SYMBOL(generic_file_fsync);
 
+/**
+ * generic_check_addressable - Check addressability of file system
+ * @blocksize_bits:	log of file system block size
+ * @num_blocks:		number of blocks in file system
+ *
+ * Determine whether a file system with @num_blocks blocks (and a
+ * block size of 2**@blocksize_bits) is addressable by the sector_t
+ * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
+ */
+int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
+{
+	u64 last_fs_block = num_blocks - 1;
+
+	if (unlikely(num_blocks == 0))
+		return 0;
+
+	if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
+		return -EINVAL;
+
+	if ((last_fs_block >
+	     (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
+	    (last_fs_block >
+	     (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - blocksize_bits))) {
+		return -EFBIG;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(generic_check_addressable);
+
 /*
  * No-op implementation of ->fsync for in-memory filesystems.
  */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e5106e4..7644248 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2414,6 +2414,8 @@ extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
 
 extern int generic_file_fsync(struct file *, int);
 
+extern int generic_check_addressable(unsigned, u64);
+
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_page(struct address_space *,
 				struct page *, struct page *);
-- 
1.7.1


-- 

"Friends may come and go, but enemies accumulate." 
        - Thomas Jones

Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127