linux-kernel - [patch] md: bitmap read

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Date:	Mon, 22 Jan 2007 16:03:51 +0800
From:	"yang yin" <yinyang801120@...il.com>
To:	linux-raid@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [patch] md: bitmap read_page error

If the bitmap size is less than one page including super_block and
bitmap and the inode's i_blkbits is also small, when doing the
read_page function call to read the sb_page, it may return a error.
For example, if the device is 12800 chunks, its bitmap file size is
about 1.6KB include the bitmap super block. But the inode i_blkbits
value of the bitmap file is 10,  the read_page will submit 4 bh to
load the sb_page. Because the size of bitmap is only 1.6KB, in the
while loop, the error will ocurr when do bmap operation for the block
2, which will  return 0. Then the bitmap can't be initated because of
ther read sb page fail.

Another error is in the bitmap_init_from_disk function.  Before doing
read_page,. calculating the count value misses the size of super
block. When the bitmap just needs one page, It will read two pages
adding the super block. But at the second read, the count value will
be set to 0, and not all the bitmap will be read from the disk and
some bitmap will missed at the second page.

I give a patch as following:

---------
diff -Nur linux-2.6.19.2.orig/drivers/md/bitmap.c
linux-2.6.19.2/drivers/md/bitmap.c
--- linux-2.6.19.2.orig/drivers/md/bitmap.c     2007-01-11
03:10:37.000000000 +0800
+++ linux-2.6.19.2/drivers/md/bitmap.c  2007-01-20 20:45:32.000000000 +0800
@@ -352,6 +352,7 @@
        struct inode *inode = file->f_dentry->d_inode;
        struct buffer_head *bh;
        sector_t block;
+       loff_t read_size = 0;

        PRINTK("read bitmap file (%dB @ %Lu)\n", (int)PAGE_SIZE,
                        (unsigned long long)index << PAGE_SHIFT);
@@ -371,7 +372,7 @@
        attach_page_buffers(page, bh);
        block = index << (PAGE_SHIFT - inode->i_blkbits);
        while (bh) {
-               if (count == 0)
+               if (count == 0 || (read_size >= (inode->i_size -
(index << PAGE_SHIFT))))
                        bh->b_blocknr = 0;
                else {
                        bh->b_blocknr = bmap(inode, block);
@@ -394,6 +395,7 @@
                        set_buffer_mapped(bh);
                        submit_bh(READ, bh);
                }
+               read_size += (1 << inode->i_blkbits);
                block++;
                bh = bh->b_this_page;
        }
@@ -877,7 +879,7 @@
                        int count;
                        /* unmap the old page, we're done with it */
                        if (index == num_pages-1)
-                               count = bytes - index * PAGE_SIZE;
+                               count = bytes + sizeof(bitmap_super_t)
- index * PAGE_SIZE;
                        else
                                count = PAGE_SIZE;
                        if (index == 0) {

yinyang

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