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SubjectRe: [PATCH 1/3] Add flag to identify block swap devices
Hi again.

On 07/05/10 17:25, Nitin Gupta wrote:
> Added SWP_BLKDEV flag to distinguish block and regular file backed
> swap devices. We could also check if a swap is entire block device,
> rather than a file, by:
> S_ISBLK(swap_info_struct->swap_file->f_mapping->host->i_mode)
> but, I think, simply checking this flag is more convenient.
>
> Signed-off-by: Nitin Gupta<ngupta@vflare.org>
> ---
> include/linux/swap.h | 1 +
> mm/swapfile.c | 1 +
> 2 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 1f59d93..ec2b7a4 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -146,6 +146,7 @@ enum {
> SWP_DISCARDING = (1<< 3), /* now discarding a free cluster */
> SWP_SOLIDSTATE = (1<< 4), /* blkdev seeks are cheap */
> SWP_CONTINUED = (1<< 5), /* swap_map has count continuation */
> + SWP_BLKDEV = (1<< 6), /* its a block device */
> /* add others here before... */
> SWP_SCANNING = (1<< 8), /* refcount in scan_swap_map */
> };
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6cd0a8f..ecb069e 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1884,6 +1884,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> if (error< 0)
> goto bad_swap;
> p->bdev = bdev;
> + p->flags |= SWP_BLKDEV;
> } else if (S_ISREG(inode->i_mode)) {
> p->bdev = inode->i_sb->s_bdev;
> mutex_lock(&inode->i_mutex);

The more I read your patches, the more I think either I'm seriously
confused (entirely possible!) or you are.

Don't you want to distinguish RAM backed swap from swap that's either a
partition or a file? If that's the case, you should also be setting
SWP_BLKDEV in the S_ISREG part that follows iff the p->bdev is a regular
file.

Regards,

Nigel


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