On 11/15/17 6:10 AM, Nikolay Borisov wrote:
> Currently the fiemap implementation of xfs_io doesn't support making ranged
> queries. This patch implements two optional arguments which take the starting
> offset and the length of the region to be queried. This also requires changing
> of the final hole range is calculated. Namely, it's now being done as
> [last_logical, logical addres of next extent] rather than being statically
> determined by [last_logical, filesize].
>
> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
Ok, so first an apology for taking so long to really, really look at this.
When I started reviewing this, and dreading the complexity of the fiemap loop
control (why /is/ it so complicated today, anyway?) I started wondering: why
do we need a lot more logic? Why can't we simply:
1) Set a non-zero mapping start
2) Set a non-maximal mapping length
3) Decrement that length as we map, and
4) When the kernel tells us mapped_extents for the range is 0, stop.
And this is what I ended up with, which seems a lot simpler. Is there any
problem with this approach?
This /almost/ passes your test; what it doesn't do is show holes at the edges
of the mapping range, but I think that's ok.
The interface itself says nothing about holes, it only maps allocated ranges.
If we ask for a ranged query, I think it's appropriate to /not/ print holes
on either side of the requested range.
Thoughts?
diff --git a/io/fiemap.c b/io/fiemap.c
index bdcfacd..bbf6d63 100644
--- a/io/fiemap.c
+++ b/io/fiemap.c
@@ -49,6 +49,8 @@ fiemap_help(void)
" -l -- also displays the length of each extent in 512-byte blocks.\n"
" -n -- query n extents.\n"
" -v -- Verbose information\n"
+" offset is the starting offset to map, and is optional. If offset is\n"
+" specified, mapping length may (optionally) be specified as well."
"\n"));
}
@@ -235,9 +237,15 @@ fiemap_f(
int boff_w = 16;
int tot_w = 5; /* 5 since its just one number */
int flg_w = 5;
- __u64 last_logical = 0;
+ __u64 last_logical = 0; /* last extent offset handled */
+ off64_t start_offset = 0; /* mapping start */
+ off64_t length = -1LL; /* mapping length */
+ off64_t range_end = -1LL; /* mapping end*/
+ size_t fsblocksize, fssectsize;
struct stat st;
+ init_cvtnum(&fsblocksize, &fssectsize);
+
while ((c = getopt(argc, argv, "aln:v")) != EOF) {
switch (c) {
case 'a':
@@ -257,6 +265,27 @@ fiemap_f(
}
}
+ /* Range start (optional) */
+ if (optind < argc) {
+ 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++;
+ }
+
+ /* Range length (optional if range start was specified) */
+ if (optind < argc) {
+ length = cvtnum(fsblocksize, fssectsize, argv[optind]);
+ if (length < 0) {
+ printf("non-numeric len argument -- %s\n", argv[optind]);
+ return 0;
+ }
+ range_end = start_offset + length;
+ }
+
map_size = sizeof(struct fiemap) +
(EXTENT_BATCH * sizeof(struct fiemap_extent));
fiemap = malloc(map_size);
@@ -274,7 +303,7 @@ fiemap_f(
memset(fiemap, 0, map_size);
fiemap->fm_flags = fiemap_flags;
fiemap->fm_start = last_logical;
- fiemap->fm_length = -1LL;
+ fiemap->fm_length = range_end - last_logical;
fiemap->fm_extent_count = EXTENT_BATCH;
ret = ioctl(file->fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
@@ -336,7 +365,8 @@ fiemap_f(
return 0;
}
- if (cur_extent && last_logical < st.st_size)
+ /* Print last hole to EOF only if range end was not specified */
+ if (cur_extent && (range_end == -1LL) && (last_logical < st.st_size))
print_hole(foff_w, boff_w, tot_w, cur_extent, lflag, !vflag,
BTOBBT(last_logical), BTOBBT(st.st_size));
@@ -353,7 +383,7 @@ 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] [offset [len]]");
fiemap_cmd.oneline = _("print block mapping for a file");
fiemap_cmd.help = fiemap_help;
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