[PATCH v4 2/2] fiemap: Implement ranged query

[Nikolay Borisov <nborisov@suse.com>]

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@suse.com>
---
V4: 
 * Don't do any fiemap processing if passed offset is past EOF. Filesystems
 might have custom handling for this. XFS for example pretends there is a 
 hole. 

 * Restore offset/len handling to using the optional params at the end of 
 getopt and not using an additional '-r' param

V3: 
 * Fixed a bug where incorrect extent index was shown if we didn't print a 
 hole. This was due to statically returning 2 at the end of print_(plain|verbose)
 Now, the actual number of printed extents inside the 2 functions is used. 
 This bug is visible only with the -r parameter

 * Fixed a bug where 1 additional extent would be printed. This was a result of 
 the aforementioned bug fix, since now printing function can return 1 and still
 have printed an extent and no hole. This can happen when you use -r parameter,
 this is now fixed and a comment explaining it is put. 

 * Reworked the handling of the new params by making them arguments to the 
 -r parameter. 

V2:
 * Incorporated Daricks feedback - removed variables which weren't introduced
  until the next patch as a result the build with this patch was broken. This is 
  fixed now
 io/fiemap.c       | 114 +++++++++++++++++++++++++++++++++++++++++++-----------
 man/man8/xfs_io.8 |   5 ++-
 2 files changed, 94 insertions(+), 25 deletions(-)

diff --git a/io/fiemap.c b/io/fiemap.c
index 08391f69d9bd..08203153b877 100644
--- a/io/fiemap.c
+++ b/io/fiemap.c
@@ -27,6 +27,9 @@
 
 static cmdinfo_t fiemap_cmd;
 static int max_extents = -1;
+static __u64 covered_length = 0;
+static __u64 len = -1LL;
+static bool range_limit = false;
 
 static void
 fiemap_help(void)
@@ -79,7 +82,7 @@ print_hole(
 		       boff_w, _("hole"), tot_w, lstart - llast);
 	   }
 
-
+	   covered_length += BBTOB(lstart - llast);
 }
 
 static int
@@ -90,7 +93,8 @@ print_verbose(
 	int			tot_w,
 	int			flg_w,
 	int			cur_extent,
-	__u64			last_logical)
+	__u64			last_logical,
+	__u64			limit)
 {
 	__u64			lstart;
 	__u64			llast;
@@ -99,6 +103,7 @@ print_verbose(
 	char			lbuf[48];
 	char			bbuf[48];
 	char			flgbuf[16];
+	int			num_printed = 0;
 
 	llast = BTOBBT(last_logical);
 	lstart = BTOBBT(extent->fe_logical);
@@ -120,10 +125,11 @@ print_verbose(
 		print_hole(foff_w, boff_w, tot_w, cur_extent, 0, false, llast,
 			   lstart);
 		cur_extent++;
+		num_printed = 1;
 	}
 
-	if (cur_extent == max_extents)
-		return 1;
+	if (cur_extent == max_extents || (range_limit && covered_length >= limit))
+		return num_printed;
 
 	snprintf(lbuf, sizeof(lbuf), "[%llu..%llu]:", lstart,
 		 lstart + len - 1ULL);
@@ -132,7 +138,9 @@ print_verbose(
 	printf("%4d: %-*s %-*s %*llu %*s\n", cur_extent, foff_w, lbuf,
 	       boff_w, bbuf, tot_w, len, flg_w, flgbuf);
 
-	return 2;
+	num_printed++;
+
+	return num_printed;
 }
 
 static int
@@ -140,12 +148,14 @@ print_plain(
 	struct fiemap_extent	*extent,
 	int			lflag,
 	int			cur_extent,
-	__u64			last_logical)
+	__u64			last_logical,
+	__u64			limit)
 {
 	__u64			lstart;
 	__u64			llast;
 	__u64			block;
 	__u64			len;
+	int			num_printed = 0;
 
 	llast = BTOBBT(last_logical);
 	lstart = BTOBBT(extent->fe_logical);
@@ -155,20 +165,23 @@ print_plain(
 	if (lstart != llast) {
 		print_hole(0, 0, 0, cur_extent, lflag, true, llast, lstart);
 		cur_extent++;
+		num_printed = 1;
 	}
 
-	if (cur_extent == max_extents)
-		return 1;
+	if (cur_extent == max_extents || (range_limit && covered_length >= limit))
+		return num_printed;
 
 	printf("\t%d: [%llu..%llu]: %llu..%llu", cur_extent,
 	       lstart, lstart + len - 1ULL, block,
 	       block + len - 1ULL);
 
+	num_printed++;
+
 	if (lflag)
 		printf(_(" %llu blocks\n"), len);
 	else
 		printf("\n");
-	return 2;
+	return num_printed;
 }
 
 /*
@@ -256,8 +269,11 @@ fiemap_f(
 	int		tot_w = 5;	/* 5 since its just one number */
 	int		flg_w = 5;
 	__u64		last_logical = 0;
+	size_t		fsblocksize, fssectsize;
 	struct stat	st;
 
+	init_cvtnum(&fsblocksize, &fssectsize);
+
 	while ((c = getopt(argc, argv, "aln:v")) != EOF) {
 		switch (c) {
 		case 'a':
@@ -277,6 +293,34 @@ 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;
+		range_limit = true;
+	}
+
+	memset(&st, 0, sizeof(st));
+	if (fstat(file->fd, &st)) {
+		fprintf(stderr, "%s: fstat failed: %s\n", progname,
+			strerror(errno));
+		exitcode = 1;
+		return 0;
+	}
+
 	map_size = sizeof(struct fiemap) +
 		(EXTENT_BATCH * sizeof(struct fiemap_extent));
 	fiemap = malloc(map_size);
@@ -289,10 +333,13 @@ fiemap_f(
 
 	printf("%s:\n", file->name);
 
+	if (last_logical >= st.st_size)
+		goto out;
+
 	while (!last && (cur_extent != max_extents)) {
 
 		ret = __fiemap(fiemap, map_size, fiemap_flags, last_logical,
-			       -1LL);
+			       len - covered_length);
 		if (ret < 0) {
 			exitcode = 1;
 			goto out;
@@ -317,14 +364,23 @@ fiemap_f(
 				num_printed = print_verbose(extent, foff_w,
 							    boff_w, tot_w,
 							    flg_w, cur_extent,
-							    last_logical);
+							    last_logical,
+							    len);
 			} else
 				num_printed = print_plain(extent, lflag,
 							  cur_extent,
-							  last_logical);
+							  last_logical,
+							  len);
 
 			cur_extent += num_printed;
 			last_logical = extent->fe_logical + extent->fe_length;
+			/* If num_printed > 0 then we dunno if we have printed
+			 * a hole or an extent and a hole but we don't really
+			 * care. Termination of the loop is still going to be
+			 * correct
+			 */
+			if (num_printed)
+				covered_length += extent->fe_length;
 
 			if (extent->fe_flags & FIEMAP_EXTENT_LAST) {
 				last = 1;
@@ -333,24 +389,36 @@ fiemap_f(
 
 			if (cur_extent == max_extents)
 				break;
+
+			if (range_limit && covered_length >= len)
+				goto out;
 		}
 	}
 
 	if (cur_extent  == max_extents)
 		goto out;
 
-	memset(&st, 0, sizeof(st));
-	if (fstat(file->fd, &st)) {
-		fprintf(stderr, "%s: fstat failed: %s\n", progname,
-			strerror(errno));
-		free(fiemap);
-		exitcode = 1;
-		return 0;
-	}
 
-	if (cur_extent && last_logical < st.st_size)
+	if (last_logical < st.st_size &&
+	    (!range_limit || covered_length < len)) {
+		int end;
+
+		ret = __fiemap(fiemap, map_size, fiemap_flags, last_logical,
+			       st.st_size);
+		if (ret < 0) {
+			exitcode = 1;
+			goto out;
+		}
+
+		if (!fiemap->fm_mapped_extents)
+			end = BTOBBT(st.st_size);
+		else
+			end = BTOBBT(fiemap->fm_extents[0].fe_logical);
+
+
 		print_hole(foff_w, boff_w, tot_w, cur_extent, lflag, !vflag,
-			   BTOBBT(last_logical), BTOBBT(st.st_size));
+			   BTOBBT(last_logical), end);
+	}
 
 out:
 	free(fiemap);
@@ -365,7 +433,7 @@ 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;
 
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 0fd9b951199c..27f1ae163913 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