2014-02-03, OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>:
> Namjae Jeon <linkinjeon@xxxxxxxxx> writes:
>
>> From: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
>>
>> Make the fibmap call the return the proper physical block number for any
>> offset request in the fallocated range.
>>
>> Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
>> Signed-off-by: Amit Sahrawat <a.sahrawat@xxxxxxxxxxx>
>> ---
>> fs/fat/cache.c | 13 ++++++++++---
>> fs/fat/fat.h | 3 +++
>> fs/fat/inode.c | 3 +++
>> 3 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/fat/cache.c b/fs/fat/cache.c
>> index a132666..d22c1a2 100644
>> --- a/fs/fat/cache.c
>> +++ b/fs/fat/cache.c
>> @@ -325,19 +325,26 @@ int fat_bmap(struct inode *inode, sector_t sector,
>> sector_t *phys,
>>
>> last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
>> if (sector >= last_block) {
>> - if (!create)
>> - return 0;
>> -
>> /*
>> * Both ->mmu_private and ->i_disksize can access
>> * on only allocation path. (caller must hold ->i_mutex)
>> */
>> last_block = (MSDOS_I(inode)->i_disksize + (blocksize - 1))
>> >> blocksize_bits;
>> + if (!create) {
>> + /* Map a block in fallocated region */
>> + if (atomic_read(&MSDOS_I(inode)->beyond_isize))
>> + if (sector < last_block)
>> + goto out_map_cluster;
>> +
>> + return 0;
>> + }
>> +
>> if (sector >= last_block)
>> return 0;
>> }
>>
>> +out_map_cluster:
>> cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
>> offset = sector & (sbi->sec_per_clus - 1);
>> cluster = fat_bmap_cluster(inode, cluster);
>> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
>> index 7b5851f..b884276 100644
>> --- a/fs/fat/fat.h
>> +++ b/fs/fat/fat.h
>> @@ -129,6 +129,9 @@ struct msdos_inode_info {
>> struct hlist_node i_dir_hash; /* hash by i_logstart */
>> struct rw_semaphore truncate_lock; /* protect bmap against truncate */
>> struct inode vfs_inode;
>> +
>> + /* for getting block number beyond file size in case of fallocate */
>> + atomic_t beyond_isize;
>> };
>>
>> struct fat_slot_info {
>> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
>> index 3636617..1c3192b 100644
>> --- a/fs/fat/inode.c
>> +++ b/fs/fat/inode.c
>> @@ -256,7 +256,10 @@ static sector_t _fat_bmap(struct address_space
>> *mapping, sector_t block)
>>
>> /* fat_get_cluster() assumes the requested blocknr isn't truncated. */
>> down_read(&MSDOS_I(mapping->host)->truncate_lock);
>> + /* To get block number beyond file size in fallocated region */
>> + atomic_set(&MSDOS_I(mapping->host)->beyond_isize, 1);
>> blocknr = generic_block_bmap(mapping, block, fat_get_block);
>> + atomic_set(&MSDOS_I(mapping->host)->beyond_isize, 0);
>> up_read(&MSDOS_I(mapping->host)->truncate_lock);
>
> This is racy. While user is using bmap, kernel can allocate new blocks.
> We should use another function for this.
I understand that fat can map fallocated blocks in read case while
user is using bmap.
But I can not find the case allocate new blocks.
If I am missing something, Could you please elaborate more ?
Is it a case of _bmap request returning the block number for block
allocated in parallel write path ?
Thanks.
>
> For example, something like
>
> fat_get_block_bmap()
> {
> [...]
> fat_get_block2(inode, iblock, &max_blocks, bh_result, create, bmap);
> [...]
> }
>
> blocknr = generic_block_bmap(mapping, block, fat_get_block_bmap);
> --
> OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
>
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