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Date: Thu, 31 Jan 2019 19:42:06 +0800
From: yangerkun <yangerkun@...wei.com>
To: Jan Kara <jack@...e.cz>
CC: <miaoxie@...wei.com>, <yi.zhang@...wei.com>, <houtao1@...wei.com>,
<linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext2: get the exact max filesize in ext2_max_size
Jan Kara wrote on 2019/1/30 0:42:
> On Wed 23-01-19 21:14:09, yangerkun wrote:
>> When mkfs.ext2 with '-b 65536' and mount(arm 64KB page size), function
>> mount_fs will trigger WARNING since ext2_max_size will return value less
>> than 0. Also, we cannot write any file in this fs since the sb->maxbytes
>> is less than 0.
>>
>> Fix it by get the exact max file size. First, get the max depth for
>> indirect blocks and check does the max data blocks add indirect blocks
>> will execced upper_limit. If right, bisect to get exact data blocks
>> number which satisfy 'data blocks number + indirect blocks number ==
>> upper_limit'.
>>
>> Signed-off-by: yangerkun <yangerkun@...wei.com>
>
> Thanks for the patches but I was really looking for something simpler.
> Something like the attached patch. Although your more precise function will
> raise the maximum file size by couple of kilobytes I don't think the
> complexity is really worth it...
Agree with you. A precise answer with so complexity function does not
make sense. Also i have review and test your without any problem. I
prefer your patch!
Reviewed-by: yangerkun <yangerkun@...wei.com>
Thanks a lot,
Kun.
>
> Honza
>
>> ---
>> fs/ext2/super.c | 115 ++++++++++++++++++++++++++++++++++++++++++++------------
>> 1 file changed, 92 insertions(+), 23 deletions(-)
>>
>> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
>> index 73b2d52..b3eb6e9 100644
>> --- a/fs/ext2/super.c
>> +++ b/fs/ext2/super.c
>> @@ -753,11 +753,16 @@ static int ext2_check_descriptors(struct super_block *sb)
>> * block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
>> * We need to be 1 filesystem block less than the 2^32 sector limit.
>> */
>> -static loff_t ext2_max_size(int bits)
>> +static loff_t ext2_max_size(struct super_block *sb, int bits)
>> {
>> - loff_t res = EXT2_NDIR_BLOCKS;
>> - int meta_blocks;
>> + loff_t res;
>> + loff_t max_meta_blocks;
>> + loff_t used_data_blocks;
>> + loff_t max_data_blocks;
>> loff_t upper_limit;
>> + int depth;
>> + loff_t high, low;
>> +
>>
>> /* This is calculated to be the largest file size for a
>> * dense, file such that the total number of
>> @@ -771,24 +776,88 @@ static loff_t ext2_max_size(int bits)
>> /* total blocks in file system block size */
>> upper_limit >>= (bits - 9);
>>
>> + /* Try to get max depth of metadata blocks */
>> + depth = 0;
>> + max_meta_blocks = 0;
>> + used_data_blocks = 0;
>> + max_data_blocks = EXT2_NDIR_BLOCKS;
>> + if (max_meta_blocks + max_data_blocks > upper_limit)
>> + goto bisect;
>> +
>> + depth++;
>> + max_meta_blocks = 1;
>> + used_data_blocks = max_data_blocks;
>> + max_data_blocks += 1LL << (bits - 2);
>> + if (max_meta_blocks + max_data_blocks > upper_limit)
>> + goto bisect;
>> +
>> + depth++;
>> + max_meta_blocks += 1 + (1LL << (bits - 2));
>> + used_data_blocks = max_data_blocks;
>> + max_data_blocks += 1LL << (2 * (bits - 2));
>> + if (max_meta_blocks + max_data_blocks > upper_limit)
>> + goto bisect;
>> +
>> + depth++;
>> + max_meta_blocks += 1 + (1LL << (bits - 2)) + (1LL << (2 * (bits - 2)));
>> + used_data_blocks = max_data_blocks;
>> + max_data_blocks += 1LL << (3 * (bits - 2));
>> + if (max_meta_blocks + max_data_blocks > upper_limit)
>> + goto bisect;
>> +
>> + goto out;
>> +bisect:
>> + low = 0;
>> + if (depth == 0)
>> + high = EXT2_NDIR_BLOCKS;
>> + else
>> + high = 1 << (depth * (bits - 2));
>> + while (low <= high) {
>> + int offsets[4];
>> + loff_t mid = (low + high) >> 1;
>> + depth = ext2_block_to_path(sb, mid + used_data_blocks - 1, offsets, NULL);
>> + if (!depth)
>> + return -EIO;
>> +
>> + max_meta_blocks = 0;
>> + if (depth == 1)
>> + max_meta_blocks = 0;
>> +
>> + if (depth == 2)
>> + max_meta_blocks = 1;
>> +
>> + if (depth == 3) {
>> + /* Indirect blocks */
>> + max_meta_blocks += 1;
>> + /* Double indirect blocks */
>> + max_meta_blocks += 1;
>> + max_meta_blocks += offsets[1];
>> + }
>>
>> - /* indirect blocks */
>> - meta_blocks = 1;
>> - /* double indirect blocks */
>> - meta_blocks += 1 + (1LL << (bits-2));
>> - /* tripple indirect blocks */
>> - meta_blocks += 1 + (1LL << (bits-2)) + (1LL << (2*(bits-2)));
>> -
>> - upper_limit -= meta_blocks;
>> - upper_limit <<= bits;
>> -
>> - res += 1LL << (bits-2);
>> - res += 1LL << (2*(bits-2));
>> - res += 1LL << (3*(bits-2));
>> - res <<= bits;
>> - if (res > upper_limit)
>> - res = upper_limit;
>> -
>> + if (depth == 4) {
>> + /* Indirect blocks */
>> + max_meta_blocks += 1;
>> + /* Double indirect blocks */
>> + max_meta_blocks += 1 + (1 << (bits - 2));
>> + /* Tripple indirect blocks */
>> + max_meta_blocks += 1;
>> + if (offsets[1])
>> + max_meta_blocks += (offsets[1] - 1) * (1 << (bits - 2));
>> +
>> + max_meta_blocks += 1;
>> + max_meta_blocks += offsets[2];
>> + }
>> + if (max_meta_blocks + mid + used_data_blocks > upper_limit)
>> + high = mid - 1;
>> + if (max_meta_blocks + mid + used_data_blocks < upper_limit)
>> + low = mid + 1;
>> + if (max_meta_blocks + mid + used_data_blocks == upper_limit) {
>> + max_data_blocks = mid + used_data_blocks;
>> + break;
>> + }
>> + }
>> +out:
>> + res = max_data_blocks << bits;
>> if (res > MAX_LFS_FILESIZE)
>> res = MAX_LFS_FILESIZE;
>>
>> @@ -995,7 +1064,9 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
>> }
>> }
>>
>> - sb->s_maxbytes = ext2_max_size(sb->s_blocksize_bits);
>> + sbi->s_addr_per_block_bits =
>> + ilog2 (EXT2_ADDR_PER_BLOCK(sb));
>> + sb->s_maxbytes = ext2_max_size(sb, sb->s_blocksize_bits);
>> sb->s_max_links = EXT2_LINK_MAX;
>>
>> if (le32_to_cpu(es->s_rev_level) == EXT2_GOOD_OLD_REV) {
>> @@ -1035,8 +1106,6 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
>> sizeof (struct ext2_group_desc);
>> sbi->s_sbh = bh;
>> sbi->s_mount_state = le16_to_cpu(es->s_state);
>> - sbi->s_addr_per_block_bits =
>> - ilog2 (EXT2_ADDR_PER_BLOCK(sb));
>> sbi->s_desc_per_block_bits =
>> ilog2 (EXT2_DESC_PER_BLOCK(sb));
>>
>> --
>> 2.9.5
>>
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