Re: [PATCH] btrfs-progs: check if device supports trim

[Eric Sandeen <sandeen@redhat.com>]

On 9/20/13 11:42 AM, David Sterba wrote:
> The message about trim was printed unconditionally, we should check if
> trim is supported at all.

Good idea, but I wonder if there's any risk that discard(0,0) will ever
be optimized away on the kernel side & pass unconditionally?

I was thinking we could get this from blkid, but maybe not.

In the meantime it does do the right thing, so:

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

> Signed-off-by: David Sterba <dsterba@suse.cz>
> ---
>  utils.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/utils.c b/utils.c
> index 5fa193b..6c74654 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -597,13 +597,16 @@ int btrfs_prepare_device(int fd, char *file, int zero_end, u64 *block_count_ret,
>  	}
>  
>  	if (discard) {
> -		fprintf(stderr, "Performing full device TRIM (%s) ...\n",
> -				pretty_size(block_count));
>  		/*
> -		 * We intentionally ignore errors from the discard ioctl.  It is
> -		 * not necessary for the mkfs functionality but just an optimization.
> +		 * We intentionally ignore errors from the discard ioctl.  It
> +		 * is not necessary for the mkfs functionality but just an
> +		 * optimization.
>  		 */
> -		discard_blocks(fd, 0, block_count);
> +		if (discard_blocks(fd, 0, 0) == 0) {
> +			fprintf(stderr, "Performing full device TRIM (%s) ...\n",
> +				pretty_size(block_count));
> +			discard_blocks(fd, 0, block_count);
> +		}
>  	}
>  
>  	ret = zero_dev_start(fd);
>