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Date: Mon, 30 May 2011 10:22:51 -0600
From: Andreas Dilger <adilger.kernel@...ger.ca>
To: Jan Kara <jack@...e.cz>
Cc: Akinobu Mita <akinobu.mita@...il.com>,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] ext3: use little-endian bitops directly
On 2011-05-30, at 8:57 AM, Jan Kara wrote:
> On Mon 30-05-11 22:47:15, Akinobu Mita wrote:
>> s/ext3_set_bit/__test_and_set_bit_le/
>> s/ext3_clear_bit/__test_and_clear_bit_le/
>> s/ext3_test_bit/test_bit_le/
>> s/ext3_find_first_zero_bit/find_first_zero_bit_le/
>> s/ext3_find_next_zero_bit/find_next_zero_bit_le/
>>
>> This change reveals that there are some __test_and_{set,clear}_bit_le()
>> calls which ignore the return value. These can be replaced with
>> __{set,clear}_bit_le().
>
> OK, after some though this is probably an improvement in readability.
> Added to my tree.
Really? There are many different varieties of bitops, and once the ext3_* bitops are removed it is no longer clear to the developer which version is the right one to use for the ext3 operations. test_and_set_bit() vs. __test_and_set_bit() vs. test_and_set_bit_lock() vs. sync_test_and_set_bit() vs. __test_and_set_bit_le() vs. test_and_set_bit_le()? I think it will lead to confusion and bugs being added to the code in the future as different types of operations are incorrectly used in the code. I doubt most kernel developers understand all of the differences between those different bitops on different architectures. What works on one arch (especially x86) may not work correctly on another arch, and corrupt the filesystem for only a small number of users, producing hard-to-debug problems.
Note that I'm all in favour of removing the ext2_{set,clear}_bit_atomic() variants of the bitops as global bitops functions, and change the ext3_{set,clear}_bit() definitions to using test_and_{set,clear}_bit() functions directly, but it makes sense to keep the ext3_*() bitops macros and their use in the code for consistency, and as a clear guide to the programmer about.
There are many examples of helper macro/inline functions to provide uniform access to low-level bitmaps, like cpumask_test_and_set_cpu(), cpu_test_and_set(), tasklet_try_lock(), zone_test_and_set_flag(), node_test_and_set(), etc. These are all in place so that there is a single uniform way of accessing and modifying these structures.
>> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
>> Cc: Jan Kara <jack@...e.cz>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
>> Cc: linux-ext4@...r.kernel.org
>> ---
>> fs/ext3/balloc.c | 20 ++++++++++----------
>> fs/ext3/ialloc.c | 8 ++++----
>> fs/ext3/inode.c | 2 +-
>> fs/ext3/resize.c | 14 +++++++-------
>> include/linux/ext3_fs.h | 5 -----
>> 5 files changed, 22 insertions(+), 27 deletions(-)
>>
>> diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
>> index fe52297..8365b3d 100644
>> --- a/fs/ext3/balloc.c
>> +++ b/fs/ext3/balloc.c
>> @@ -112,21 +112,21 @@ static int ext3_valid_block_bitmap(struct super_block *sb,
>> /* check whether block bitmap block number is set */
>> bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
>> offset = bitmap_blk - group_first_block;
>> - if (!ext3_test_bit(offset, bh->b_data))
>> + if (!test_bit_le(offset, bh->b_data))
>> /* bad block bitmap */
>> goto err_out;
>>
>> /* check whether the inode bitmap block number is set */
>> bitmap_blk = le32_to_cpu(desc->bg_inode_bitmap);
>> offset = bitmap_blk - group_first_block;
>> - if (!ext3_test_bit(offset, bh->b_data))
>> + if (!test_bit_le(offset, bh->b_data))
>> /* bad block bitmap */
>> goto err_out;
>>
>> /* check whether the inode table block number is set */
>> bitmap_blk = le32_to_cpu(desc->bg_inode_table);
>> offset = bitmap_blk - group_first_block;
>> - next_zero_bit = ext3_find_next_zero_bit(bh->b_data,
>> + next_zero_bit = find_next_zero_bit_le(bh->b_data,
>> offset + EXT3_SB(sb)->s_itb_per_group,
>> offset);
>> if (next_zero_bit >= offset + EXT3_SB(sb)->s_itb_per_group)
>> @@ -722,14 +722,14 @@ static int ext3_test_allocatable(ext3_grpblk_t nr, struct buffer_head *bh)
>> int ret;
>> struct journal_head *jh = bh2jh(bh);
>>
>> - if (ext3_test_bit(nr, bh->b_data))
>> + if (test_bit_le(nr, bh->b_data))
>> return 0;
>>
>> jbd_lock_bh_state(bh);
>> if (!jh->b_committed_data)
>> ret = 1;
>> else
>> - ret = !ext3_test_bit(nr, jh->b_committed_data);
>> + ret = !test_bit_le(nr, jh->b_committed_data);
>> jbd_unlock_bh_state(bh);
>> return ret;
>> }
>> @@ -752,14 +752,14 @@ bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
>> struct journal_head *jh = bh2jh(bh);
>>
>> while (start < maxblocks) {
>> - next = ext3_find_next_zero_bit(bh->b_data, maxblocks, start);
>> + next = find_next_zero_bit_le(bh->b_data, maxblocks, start);
>> if (next >= maxblocks)
>> return -1;
>> if (ext3_test_allocatable(next, bh))
>> return next;
>> jbd_lock_bh_state(bh);
>> if (jh->b_committed_data)
>> - start = ext3_find_next_zero_bit(jh->b_committed_data,
>> + start = find_next_zero_bit_le(jh->b_committed_data,
>> maxblocks, next);
>> jbd_unlock_bh_state(bh);
>> }
>> @@ -798,7 +798,7 @@ find_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
>> ext3_grpblk_t end_goal = (start + 63) & ~63;
>> if (end_goal > maxblocks)
>> end_goal = maxblocks;
>> - here = ext3_find_next_zero_bit(bh->b_data, end_goal, start);
>> + here = find_next_zero_bit_le(bh->b_data, end_goal, start);
>> if (here < end_goal && ext3_test_allocatable(here, bh))
>> return here;
>> ext3_debug("Bit not found near goal\n");
>> @@ -845,7 +845,7 @@ claim_block(spinlock_t *lock, ext3_grpblk_t block, struct buffer_head *bh)
>> if (ext3_set_bit_atomic(lock, block, bh->b_data))
>> return 0;
>> jbd_lock_bh_state(bh);
>> - if (jh->b_committed_data && ext3_test_bit(block,jh->b_committed_data)) {
>> + if (jh->b_committed_data && test_bit_le(block, jh->b_committed_data)) {
>> ext3_clear_bit_atomic(lock, block, bh->b_data);
>> ret = 0;
>> } else {
>> @@ -1697,7 +1697,7 @@ allocated:
>> int i;
>>
>> for (i = 0; i < num; i++) {
>> - if (ext3_test_bit(grp_alloc_blk+i,
>> + if (test_bit_le(grp_alloc_blk + i,
>> bh2jh(bitmap_bh)->b_committed_data)) {
>> printk("%s: block was unexpectedly set in "
>> "b_committed_data\n", __func__);
>> diff --git a/fs/ext3/ialloc.c b/fs/ext3/ialloc.c
>> index bfc2dc4..8796fbc 100644
>> --- a/fs/ext3/ialloc.c
>> +++ b/fs/ext3/ialloc.c
>> @@ -460,7 +460,7 @@ struct inode *ext3_new_inode(handle_t *handle, struct inode * dir,
>> ino = 0;
>>
>> repeat_in_this_group:
>> - ino = ext3_find_next_zero_bit((unsigned long *)
>> + ino = find_next_zero_bit_le(
>> bitmap_bh->b_data, EXT3_INODES_PER_GROUP(sb), ino);
>> if (ino < EXT3_INODES_PER_GROUP(sb)) {
>>
>> @@ -654,7 +654,7 @@ struct inode *ext3_orphan_get(struct super_block *sb, unsigned long ino)
>> * is a valid orphan (no e2fsck run on fs). Orphans also include
>> * inodes that were being truncated, so we can't check i_nlink==0.
>> */
>> - if (!ext3_test_bit(bit, bitmap_bh->b_data))
>> + if (!test_bit_le(bit, bitmap_bh->b_data))
>> goto bad_orphan;
>>
>> inode = ext3_iget(sb, ino);
>> @@ -680,9 +680,9 @@ iget_failed:
>> bad_orphan:
>> ext3_warning(sb, __func__,
>> "bad orphan inode %lu! e2fsck was run?", ino);
>> - printk(KERN_NOTICE "ext3_test_bit(bit=%d, block=%llu) = %d\n",
>> + printk(KERN_NOTICE "test_bit_le(bit=%d, block=%llu) = %d\n",
>> bit, (unsigned long long)bitmap_bh->b_blocknr,
>> - ext3_test_bit(bit, bitmap_bh->b_data));
>> + test_bit_le(bit, bitmap_bh->b_data));
>> printk(KERN_NOTICE "inode=%p\n", inode);
>> if (inode) {
>> printk(KERN_NOTICE "is_bad_inode(inode)=%d\n",
>> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
>> index 3451d23..57432a6 100644
>> --- a/fs/ext3/inode.c
>> +++ b/fs/ext3/inode.c
>> @@ -2727,7 +2727,7 @@ static int __ext3_get_inode_loc(struct inode *inode,
>> for (i = start; i < start + inodes_per_buffer; i++) {
>> if (i == inode_offset)
>> continue;
>> - if (ext3_test_bit(i, bitmap_bh->b_data))
>> + if (test_bit_le(i, bitmap_bh->b_data))
>> break;
>> }
>> brelse(bitmap_bh);
>> diff --git a/fs/ext3/resize.c b/fs/ext3/resize.c
>> index 7916e4c..213a794 100644
>> --- a/fs/ext3/resize.c
>> +++ b/fs/ext3/resize.c
>> @@ -148,7 +148,7 @@ static void mark_bitmap_end(int start_bit, int end_bit, char *bitmap)
>>
>> ext3_debug("mark end bits +%d through +%d used\n", start_bit, end_bit);
>> for (i = start_bit; i < ((start_bit + 7) & ~7UL); i++)
>> - ext3_set_bit(i, bitmap);
>> + __test_and_set_bit_le(i, bitmap);
>> if (i < end_bit)
>> memset(bitmap + (i >> 3), 0xff, (end_bit - i) >> 3);
>> }
>> @@ -222,7 +222,7 @@ static int setup_new_group_blocks(struct super_block *sb,
>>
>> if (ext3_bg_has_super(sb, input->group)) {
>> ext3_debug("mark backup superblock %#04lx (+0)\n", start);
>> - ext3_set_bit(0, bh->b_data);
>> + __test_and_set_bit_le(0, bh->b_data);
>> }
>>
>> /* Copy all of the GDT blocks into the backup in this group */
>> @@ -254,7 +254,7 @@ static int setup_new_group_blocks(struct super_block *sb,
>> brelse(gdb);
>> goto exit_bh;
>> }
>> - ext3_set_bit(bit, bh->b_data);
>> + __test_and_set_bit_le(bit, bh->b_data);
>> brelse(gdb);
>> }
>>
>> @@ -278,15 +278,15 @@ static int setup_new_group_blocks(struct super_block *sb,
>> brelse(gdb);
>> goto exit_bh;
>> }
>> - ext3_set_bit(bit, bh->b_data);
>> + __test_and_set_bit_le(bit, bh->b_data);
>> brelse(gdb);
>> }
>> ext3_debug("mark block bitmap %#04x (+%ld)\n", input->block_bitmap,
>> input->block_bitmap - start);
>> - ext3_set_bit(input->block_bitmap - start, bh->b_data);
>> + __test_and_set_bit_le(input->block_bitmap - start, bh->b_data);
>> ext3_debug("mark inode bitmap %#04x (+%ld)\n", input->inode_bitmap,
>> input->inode_bitmap - start);
>> - ext3_set_bit(input->inode_bitmap - start, bh->b_data);
>> + __test_and_set_bit_le(input->inode_bitmap - start, bh->b_data);
>>
>> /* Zero out all of the inode table blocks */
>> for (i = 0, block = input->inode_table, bit = block - start;
>> @@ -309,7 +309,7 @@ static int setup_new_group_blocks(struct super_block *sb,
>> goto exit_bh;
>> }
>> brelse(it);
>> - ext3_set_bit(bit, bh->b_data);
>> + __test_and_set_bit_le(bit, bh->b_data);
>> }
>>
>> err = extend_or_restart_transaction(handle, 2, bh);
>> diff --git a/include/linux/ext3_fs.h b/include/linux/ext3_fs.h
>> index 5e06acf..6caadd0 100644
>> --- a/include/linux/ext3_fs.h
>> +++ b/include/linux/ext3_fs.h
>> @@ -418,13 +418,8 @@ struct ext3_inode {
>> #define EXT2_MOUNT_DATA_FLAGS EXT3_MOUNT_DATA_FLAGS
>> #endif
>>
>> -#define ext3_set_bit __test_and_set_bit_le
>> #define ext3_set_bit_atomic ext2_set_bit_atomic
>> -#define ext3_clear_bit __test_and_clear_bit_le
>> #define ext3_clear_bit_atomic ext2_clear_bit_atomic
>> -#define ext3_test_bit test_bit_le
>> -#define ext3_find_first_zero_bit find_first_zero_bit_le
>> -#define ext3_find_next_zero_bit find_next_zero_bit_le
>>
>> /*
>> * Maximal mount counts between two filesystem checks
>> --
>> 1.7.4.4
>>
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
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