On Mon, Aug 16, 2010 at 09:44:35AM -0500, Eric Sandeen wrote:
> Joel Becker wrote:
> > How about:
> >
> > u64 last_fs_page = last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);
> >
> > ... ||
> > (last_fs_page > (pgoff_t)(~0ULL))) {
> >
> > Is that more readable?
>
> To me, yes. Maybe do similar for last_fs_sector.
last_fs_sector would be shifting up, which could wrap a really
large last_fs_blocks. So I'm going to keep the sector_t check as-is.
How's this:
>From 8de5cb9164cdc179ba84a07b282a895d0eb794b0 Mon Sep 17 00:00:00 2001
>From: Joel Becker <joel.becker@xxxxxxxxxx>
Date: Mon, 16 Aug 2010 12:10:17 -0700
Subject: [PATCH] libfs: Fix shift bug in generic_check_addressable()
generic_check_addressable() erroneously shifts pages down by a block
factor when it should be shifting up. To prevent overflow, we shift
blocks down to pages.
Signed-off-by: Joel Becker <joel.becker@xxxxxxxxxx>
---
fs/libfs.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/libfs.c b/fs/libfs.c
index 8debe7b..62baa03 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -925,6 +925,8 @@ EXPORT_SYMBOL(generic_file_fsync);
int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
{
u64 last_fs_block = num_blocks - 1;
+ u64 last_fs_page =
+ last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);
if (unlikely(num_blocks == 0))
return 0;
@@ -932,10 +934,8 @@ int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
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))) {
+ if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
+ (last_fs_page > (pgoff_t)(~0ULL))) {
return -EFBIG;
}
return 0;
--
1.7.1
--
Life's Little Instruction Book #267
"Lie on your back and look at the stars."
Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker@xxxxxxxxxx
Phone: (650) 506-8127
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