[PATCH RFC] fsx: support unshare range fallocate mode

[Brian Foster <bfoster@redhat.com>]

The fallocate unshare mode flag modifies traditional preallocate
mode to unshare any shared extents backing the target range. Without
the unshare flag, preallocate mode simply assures that blocks are
physically allocated, regardless of whether they might be shared.
Unshare mode behaves the same as preallocate mode outside of the
shared extent case.

Since unshare is fundamentally a modifier to preallocate mode,
enable it via an operation flag. Similar to keep size mode, select
it randomly for fallocate operations and track it via a flag and
string combination for operation logging and replay.

Unshare is mainly used for filesystems that support reflink, but the
operation is equivalent to preallocate mode for non-shared ranges,
so enable it by default. Filesystems that do not support the
fallocate flag (such as those that might not support reflink) will
fail the test operation and disable unshare calls at runtime. Also
provide a new command line option to explicitly disable unshare
calls.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---

Hi all,

A couple quick notes..

First, this applies on top of the currently pending EOF pollution
patches [1] to fsx.

Second, this triggers multiple new test failures in my initial tests
that I've not fully diagnosed. I'm not necessarily sure that we want to
hold off on added test coverage for that reason, but I'd like to at
least be sure this isn't due to this patch doing something blatantly
wrong.

That said, this has also uncovered one or two unshare related issues, so
I'm posting this slightly prematurely in order to share it and hopefully
get some review..

Brian

[1] https://lore.kernel.org/fstests/20240828181534.41054-1-bfoster@redhat.com/

 ltp/fsx.c | 59 ++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 45 insertions(+), 14 deletions(-)

diff --git a/ltp/fsx.c b/ltp/fsx.c
index 1ba1bf65..003990db 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -45,9 +45,14 @@
 
 #define NUMPRINTCOLUMNS 32	/* # columns of data to print on each line */
 
-/* Operation flags */
-
-enum opflags { FL_NONE = 0, FL_SKIPPED = 1, FL_CLOSE_OPEN = 2, FL_KEEP_SIZE = 4 };
+/* Operation flags (bitmask) */
+enum opflags {
+	FL_NONE = 0,
+	FL_SKIPPED = 1,
+	FL_CLOSE_OPEN = 2,
+	FL_KEEP_SIZE = 4,
+	FL_UNSHARE = 8
+};
 
 /*
  *	A log entry is an operation and a bunch of arguments.
@@ -167,6 +172,7 @@ int	seed = 1;			/* -S flag */
 int     mapped_writes = 1;              /* -W flag disables */
 int     fallocate_calls = 1;            /* -F flag disables */
 int     keep_size_calls = 1;            /* -K flag disables */
+int	unshare_calls = 1;		/* -u flag disables */
 int     punch_hole_calls = 1;           /* -H flag disables */
 int     zero_range_calls = 1;           /* -z flag disables */
 int	collapse_range_calls = 1;	/* -C flag disables */
@@ -543,6 +549,8 @@ logdump(void)
 				fprintf(logopsf, " keep_size");
 			if (lp->flags & FL_CLOSE_OPEN)
 				fprintf(logopsf, " close_open");
+			if (lp->flags & FL_UNSHARE)
+				fprintf(logopsf, " unshare");
 			if (overlap)
 				fprintf(logopsf, " *");
 			fprintf(logopsf, "\n");
@@ -1879,15 +1887,25 @@ do_copy_range(unsigned offset, unsigned length, unsigned dest)
 #ifdef HAVE_LINUX_FALLOC_H
 /* fallocate is basically a no-op unless extending, then a lot like a truncate */
 void
-do_preallocate(unsigned offset, unsigned length, int keep_size)
+do_preallocate(unsigned offset, unsigned length, int keep_size, int unshare)
 {
 	unsigned end_offset;
+	enum opflags opflags = FL_NONE;
+	int mode = 0;
+
+	if (keep_size) {
+		opflags |= FL_KEEP_SIZE;
+		mode |= FALLOC_FL_KEEP_SIZE;
+	}
+	if (unshare) {
+		opflags |= FL_UNSHARE;
+		mode |= FALLOC_FL_UNSHARE_RANGE;
+	}
 
         if (length == 0) {
                 if (!quiet && testcalls > simulatedopcount)
                         prt("skipping zero length fallocate\n");
-                log4(OP_FALLOCATE, offset, length, FL_SKIPPED |
-		     (keep_size ? FL_KEEP_SIZE : FL_NONE));
+                log4(OP_FALLOCATE, offset, length, FL_SKIPPED | opflags);
                 return;
         }
 
@@ -1905,8 +1923,7 @@ do_preallocate(unsigned offset, unsigned length, int keep_size)
 	 * 	1: extending prealloc
 	 * 	2: interior prealloc
 	 */
-	log4(OP_FALLOCATE, offset, length,
-	     keep_size ? FL_KEEP_SIZE : FL_NONE);
+	log4(OP_FALLOCATE, offset, length, opflags);
 
 	if (end_offset > file_size) {
 		memset(good_buf + file_size, '\0', end_offset - file_size);
@@ -1921,7 +1938,7 @@ do_preallocate(unsigned offset, unsigned length, int keep_size)
 		      end_offset <= monitorend)))
 		prt("%lld falloc\tfrom 0x%x to 0x%x (0x%x bytes)\n", testcalls,
 				offset, offset + length, length);
-	if (fallocate(fd, keep_size ? FALLOC_FL_KEEP_SIZE : 0, (loff_t)offset, (loff_t)length) == -1) {
+	if (fallocate(fd, mode, (loff_t)offset, (loff_t)length) == -1) {
 	        prt("fallocate: 0x%x to 0x%x\n", offset, offset + length);
 		prterr("do_preallocate: fallocate");
 		report_failure(161);
@@ -1929,7 +1946,7 @@ do_preallocate(unsigned offset, unsigned length, int keep_size)
 }
 #else
 void
-do_preallocate(unsigned offset, unsigned length, int keep_size)
+do_preallocate(unsigned offset, unsigned length, int keep_size, int unshare)
 {
 	return;
 }
@@ -2095,6 +2112,8 @@ read_op(struct log_entry *log_entry)
 				log_entry->flags |= FL_KEEP_SIZE;
 			else if (strcmp(str, "close_open") == 0)
 				log_entry->flags |= FL_CLOSE_OPEN;
+			else if (strcmp(str, "unshare") == 0)
+				log_entry->flags |= FL_UNSHARE;
 			else if (strcmp(str, "*") == 0)
 				;  /* overlap marker; ignore */
 			else
@@ -2161,6 +2180,7 @@ test(void)
 	unsigned long	rv;
 	unsigned long	op;
 	int		keep_size = 0;
+	int		unshare = 0;
 
 	if (simulatedopcount > 0 && testcalls == simulatedopcount)
 		writefileimage();
@@ -2190,6 +2210,7 @@ test(void)
 			offset2 = log_entry.args[2];
 			closeopen = !!(log_entry.flags & FL_CLOSE_OPEN);
 			keep_size = !!(log_entry.flags & FL_KEEP_SIZE);
+			unshare = !!(log_entry.flags & FL_UNSHARE);
 			goto have_op;
 		}
 		return 0;
@@ -2219,8 +2240,12 @@ test(void)
 			size = random() % maxfilelen;
 		break;
 	case OP_FALLOCATE:
-		if (fallocate_calls && size && keep_size_calls)
-			keep_size = random() % 2;
+		if (fallocate_calls && size) {
+			if (keep_size_calls)
+				keep_size = random() % 2;
+			if (unshare_calls)
+				unshare = random() % 2;
+		}
 		break;
 	case OP_ZERO_RANGE:
 		if (zero_range_calls && size && keep_size_calls)
@@ -2334,7 +2359,7 @@ have_op:
 
 	case OP_FALLOCATE:
 		TRIM_OFF_LEN(offset, size, maxfilelen);
-		do_preallocate(offset, size, keep_size);
+		do_preallocate(offset, size, keep_size, unshare);
 		break;
 
 	case OP_PUNCH_HOLE:
@@ -2469,6 +2494,7 @@ usage(void)
 	-r readbdy: 4096 would make reads page aligned (default 1)\n\
 	-s style: 1 gives smaller truncates (default 0)\n\
 	-t truncbdy: 4096 would make truncates page aligned (default 1)\n\
+	-u Do not use unshare range\n\
 	-w writebdy: 4096 would make writes page aligned (default 1)\n\
 	-x: preallocate file space before starting, XFS only\n\
 	-y: synchronize changes to a file\n"
@@ -2853,7 +2879,7 @@ main(int argc, char **argv)
 	setvbuf(stdout, (char *)0, _IOLBF, 0); /* line buffered stdout */
 
 	while ((ch = getopt_long(argc, argv,
-				 "0b:c:de:fg:i:j:kl:m:no:p:qr:s:t:w:xyABD:EFJKHzCILN:OP:RS:UWXZ",
+				 "0b:c:de:fg:i:j:kl:m:no:p:qr:s:t:uw:xyABD:EFJKHzCILN:OP:RS:UWXZ",
 				 longopts, NULL)) != EOF)
 		switch (ch) {
 		case 'b':
@@ -2952,6 +2978,9 @@ main(int argc, char **argv)
 			if (truncbdy <= 0)
 				usage();
 			break;
+		case 'u':
+			unshare_calls = 0;
+			break;
 		case 'w':
 			writebdy = getnum(optarg, &endp);
 			if (writebdy <= 0)
@@ -3242,6 +3271,8 @@ main(int argc, char **argv)
 		fallocate_calls = test_fallocate(0);
 	if (keep_size_calls)
 		keep_size_calls = test_fallocate(FALLOC_FL_KEEP_SIZE);
+	if (unshare_calls)
+		unshare_calls = test_fallocate(FALLOC_FL_UNSHARE_RANGE);
 	if (punch_hole_calls)
 		punch_hole_calls = test_fallocate(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE);
 	if (zero_range_calls)
-- 
2.45.0