linux-kernel - Re: [PATCH v3 5/6] fat: permit to return phy block number by fibmap in fallocated region

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Date:	Mon, 03 Feb 2014 13:26:21 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v3 5/6] fat: permit to return phy block number by fibmap in fallocated region

Namjae Jeon <linkinjeon@...il.com> writes:

> From: Namjae Jeon <namjae.jeon@...sung.com>
>
> 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@...sung.com>
> Signed-off-by: Amit Sahrawat <a.sahrawat@...sung.com>
> ---
>  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.

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@...l.parknet.co.jp>
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