Re: [PATCH v2] fiemap: Allow to specify range to fiemap

Darrick J. Wong
2017-08-10T16:13:31Z

On Thu, Aug 10, 2017 at 03:30:41PM +0300, Nikolay Borisov wrote:
> Add 2 additional, optional, arguments to the embedded fiemap command,
> that way one can specify exact ranges to be fiemapped. This will be used
> for a btrfs test. Since the arguments are optional, omitting them just
> retains the old behavior.
>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>
> Changes since v1:
> * Added help in man describing the new options
> * Removed whitespace damage
> * Simplified/dedup the code used to get the parameters in
> * Updated one line help to indicate that len param can't exist on its own
>
> io/fiemap.c | 28 ++++++++++++++++++++++++++--
> man/man8/xfs_io.8 | 5 +++--
> 2 files changed, 29 insertions(+), 4 deletions(-)
>
> diff --git a/io/fiemap.c b/io/fiemap.c
> index 75e882057362..2a0698e9d1e9 100644
> --- a/io/fiemap.c
> +++ b/io/fiemap.c
> @@ -34,6 +34,7 @@ fiemap_help(void)
> "\n"
> " Example:\n"
> " 'fiemap -v' - tabular format verbose map\n"
> +" 'fiemap 0 4k' - print fiemap extents for 0-4k range\n"
> "\n"
> " fiemap prints the map of disk blocks used by the current file.\n"
> " The map lists each extent used by the file, as well as regions in the\n"
> @@ -216,7 +217,11 @@ fiemap_f(
> int flg_w = 5;
> __u64 blocksize = 512;
> __u64 last_logical = 0;
> + __u64 len = -1LL;
> struct stat st;
> + size_t fsblocksize, fssectsize;
> +
> + init_cvtnum(&fsblocksize, &fssectsize);
>
> while ((c = getopt(argc, argv, "aln:v")) != EOF) {
> switch (c) {
> @@ -237,6 +242,25 @@ fiemap_f(
> }
> }
>
> + if (optind < argc) {
> + off64_t start_offset = cvtnum(fsblocksize, fssectsize, argv[optind]);
> + if (start_offset < 0) {
> + printf("non-numeric offset argument -- %s\n", argv[optind]);
> + return 0;
> + }
> + last_logical = start_offset;
> + optind++;
> + }
> +
> + if (optind < argc) {
> + off64_t length = cvtnum(fsblocksize, fssectsize, argv[optind]);
> + if (length < 0) {
> + printf("non-numeric len argument -- %s\n", argv[optind]);
> + return 0;
> + }
> + len = length;
> + }
> +
> if (max_extents)
> num_extents = min(num_extents, max_extents);
> map_size = sizeof(struct fiemap) +
> @@ -259,7 +283,7 @@ fiemap_f(
> memset(fiemap, 0, map_size);
> fiemap->fm_flags = fiemap_flags;
> fiemap->fm_start = last_logical;
> - fiemap->fm_length = -1LL;
> + fiemap->fm_length = len;

We don't decrement len each time through the ioctl loop? Doesn't that
cause us to request and retrieve rows for ranges we don't want?

--D

> fiemap->fm_extent_count = num_extents;
>
> ret = ioctl(file->fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
> @@ -350,7 +374,7 @@ fiemap_init(void)
> fiemap_cmd.argmin = 0;
> fiemap_cmd.argmax = -1;
> fiemap_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
> - fiemap_cmd.args = _("[-alv] [-n nx]");
> + fiemap_cmd.args = _("[-alv] [-n nx] [start offset [len]]");
> fiemap_cmd.oneline = _("print block mapping for a file");
> fiemap_cmd.help = fiemap_help;
>
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index 273b9c54c52d..125db9181851 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -295,11 +295,12 @@ Prints the block mapping for the current open file. Refer to the
> .BR xfs_bmap (8)
> manual page for complete documentation.
> .TP
> -.BI "fiemap [ \-alv ] [ \-n " nx " ]"
> +.BI "fiemap [ \-alv ] [ \-n " nx " ] [ " offset " [ " len " ]]"
> Prints the block mapping for the current open file using the fiemap
> ioctl. Options behave as described in the
> .BR xfs_bmap (8)
> -manual page.
> +manual page. Optionally, this command also supports passing the start offset
> +from where to begin the fiemap and the length of that region.
> .TP
> .BI "fsmap [ \-d | \-l | \-r ] [ \-m | \-v ] [ \-n " nx " ] [ " start " ] [ " end " ]
> Prints the mapping of disk blocks used by the filesystem hosting the current
> --
> 2.7.4
>
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