linux-ext4 - Re: [PATCH] filefrag: count optimize non-verbose mode; count 0 extents properly when verbose

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Date:	Thu, 09 Dec 2010 11:19:04 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] filefrag: count optimize non-verbose mode; count 0 extents
 properly when verbose

On 11/23/10 5:21 PM, Eric Sandeen wrote:
> # rm -f a; touch a; filefrag -v a
> 
> yields 1 extent when it should be 0.  Without -v, 0 is returned.
> 
> Fix this up by special-casing no extents returned in verbose
> mode; skip printing the header for the columns too, since there
> are no columns to print.
> 
> Also, in nonverbose mode we can set fm_extent_count to 0
> so that FIEMAP will just query the extent count without gathering
> details; as it is today I think a non-verbose query may under-report
> the extent count once "count" extents have been filled in.
> 
> Addresses-redhat-bugzilla: 653234
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>

Ted, wondering if you can push this one in as well, if it looks ok;
I'd like to get it upstream before adding it to our package for the
above bug.

Thanks,
-Eric

> ---
> 
> diff --git a/misc/filefrag.c b/misc/filefrag.c
> index bd4486d..a48b9b0 100644
> --- a/misc/filefrag.c
> +++ b/misc/filefrag.c
> @@ -194,7 +194,14 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents)
>  	do {
>  		fiemap->fm_length = ~0ULL;
>  		fiemap->fm_flags = flags;
> -		fiemap->fm_extent_count = count;
> +		/*
> +		 * If fm_extent_count == 0, FIEMAP returns count of
> +		 * extents found without filling in details.
> +		 */
> +		if (!verbose)
> +			fiemap->fm_extent_count = 0;
> +		else
> +			fiemap->fm_extent_count = count;
>  		rc = ioctl(fd, FS_IOC_FIEMAP, (unsigned long) fiemap);
>  		if (rc < 0) {
>  			if (errno == EBADR && fiemap_incompat_printed == 0) {
> @@ -206,6 +213,14 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents)
>  		}
>  
>  		if (verbose && !fiemap_header_printed) {
> +			/*
> +			 * No extents on first call?
> +			 * Skip header and show 0 extents.
> +			 */
> +			if (fiemap->fm_mapped_extents == 0) {
> +				*num_extents = 0;
> +				goto out;
> +			}
>  			printf(" ext %*s %*s %*s length flags\n", logical_width,
>  			       "logical", physical_width, "physical",
>  			       physical_width, "expected");
> --
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