[PATCH v3 04/13] ltp/fsx.c: Add atomic writes support to fsx

Ojaswin Mujoo
2025-07-12T14:13:19Z

Implement atomic write support to help fuzz atomic writes
with fsx.

Suggested-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
---
ltp/fsx.c | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 104 insertions(+), 5 deletions(-)

diff --git a/ltp/fsx.c b/ltp/fsx.c
index 163b9453..ea39ca29 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -40,6 +40,7 @@
#include <liburing.h>
#endif
#include <sys/syscall.h>
+#include "statx.h"

#ifndef MAP_FILE
# define MAP_FILE 0
@@ -49,6 +50,10 @@
#define RWF_DONTCACHE 0x80
#endif

+#ifndef RWF_ATOMIC
+#define RWF_ATOMIC 0x40
+#endif
+
#define NUMPRINTCOLUMNS 32 /* # columns of data to print on each line */

/* Operation flags (bitmask) */
@@ -110,6 +115,7 @@ enum {
OP_READ_DONTCACHE,
OP_WRITE,
OP_WRITE_DONTCACHE,
+ OP_WRITE_ATOMIC,
OP_MAPREAD,
OP_MAPWRITE,
OP_MAX_LITE,
@@ -200,6 +206,11 @@ int uring = 0;
int mark_nr = 0;
int dontcache_io = 1;
int hugepages = 0; /* -h flag */
+int do_atomic_writes = 1; /* -a flag disables */
+
+/* User for atomic writes */
+int awu_min = 0;
+int awu_max = 0;

/* Stores info needed to periodically collapse hugepages */
struct hugepages_collapse_info {
@@ -288,6 +299,7 @@ static const char *op_names[] = {
[OP_READ_DONTCACHE] = "read_dontcache",
[OP_WRITE] = "write",
[OP_WRITE_DONTCACHE] = "write_dontcache",
+ [OP_WRITE_ATOMIC] = "write_atomic",
[OP_MAPREAD] = "mapread",
[OP_MAPWRITE] = "mapwrite",
[OP_TRUNCATE] = "truncate",
@@ -422,6 +434,7 @@ logdump(void)
prt("\t***RRRR***");
break;
case OP_WRITE_DONTCACHE:
+ case OP_WRITE_ATOMIC:
case OP_WRITE:
prt("WRITE 0x%x thru 0x%x\t(0x%x bytes)",
lp->args[0], lp->args[0] + lp->args[1] - 1,
@@ -1073,6 +1086,25 @@ update_file_size(unsigned offset, unsigned size)
file_size = offset + size;
}

+static int is_power_of_2(unsigned n) {
+ return ((n & (n - 1)) == 0);
+}
+
+/*
+ * Round down n to nearest power of 2.
+ * If n is already a power of 2, return n;
+ */
+static int rounddown_pow_of_2(int n) {
+ int i = 0;
+
+ if (is_power_of_2(n))
+ return n;
+
+ for (; (1 << i) < n; i++);
+
+ return 1 << (i - 1);
+}
+
void
dowrite(unsigned offset, unsigned size, int flags)
{
@@ -1081,6 +1113,27 @@ dowrite(unsigned offset, unsigned size, int flags)
offset -= offset % writebdy;
if (o_direct)
size -= size % writebdy;
+ if (flags & RWF_ATOMIC) {
+ /* atomic write len must be inbetween awu_min and awu_max */
+ if (size < awu_min)
+ size = awu_min;
+ if (size > awu_max)
+ size = awu_max;
+
+ /* atomic writes need power-of-2 sizes */
+ size = rounddown_pow_of_2(size);
+
+ /* atomic writes need naturally aligned offsets */
+ offset -= offset % size;
+
+ /* Skip the write if we are crossing max filesize */
+ if ((offset + size) > maxfilelen) {
+ if (!quiet && testcalls > simulatedopcount)
+ prt("skipping atomic write past maxfilelen\n");
+ log4(OP_WRITE_ATOMIC, offset, size, FL_SKIPPED);
+ return;
+ }
+ }
if (size == 0) {
if (!quiet && testcalls > simulatedopcount && !o_direct)
prt("skipping zero size write\n");
@@ -1088,7 +1141,10 @@ dowrite(unsigned offset, unsigned size, int flags)
return;
}

- log4(OP_WRITE, offset, size, FL_NONE);
+ if (flags & RWF_ATOMIC)
+ log4(OP_WRITE_ATOMIC, offset, size, FL_NONE);
+ else
+ log4(OP_WRITE, offset, size, FL_NONE);

gendata(original_buf, good_buf, offset, size);
if (offset + size > file_size) {
@@ -1108,8 +1164,9 @@ dowrite(unsigned offset, unsigned size, int flags)
(monitorstart == -1 ||
(offset + size > monitorstart &&
(monitorend == -1 || offset <= monitorend))))))
- prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d\n", testcalls,
- offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0);
+ prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\tdontcache=%d atomic_wr=%d\n", testcalls,
+ offset, offset + size - 1, size, (flags & RWF_DONTCACHE) != 0,
+ (flags & RWF_ATOMIC) != 0);
iret = fsxwrite(fd, good_buf + offset, size, offset, flags);
if (iret != size) {
if (iret == -1)
@@ -1785,6 +1842,30 @@ do_dedupe_range(unsigned offset, unsigned length, unsigned dest)
}
#endif

+int test_atomic_writes(void) {
+ int ret;
+ struct statx stx;
+
+ ret = xfstests_statx(AT_FDCWD, fname, 0, STATX_WRITE_ATOMIC, &stx);
+ if (ret < 0) {
+ fprintf(stderr, "main: Statx failed with %d."
+ " Failed to determine atomic write limits, "
+ " disabling!\n", ret);
+ return 0;
+ }
+
+ if (stx.stx_attributes & STATX_ATTR_WRITE_ATOMIC &&
+ stx.stx_atomic_write_unit_min > 0) {
+ awu_min = stx.stx_atomic_write_unit_min;
+ awu_max = stx.stx_atomic_write_unit_max;
+ return 1;
+ }
+
+ fprintf(stderr, "main: IO Stack does not support "
+ "atomic writes, disabling!\n");
+ return 0;
+}
+
#ifdef HAVE_COPY_FILE_RANGE
int
test_copy_range(void)
@@ -2356,6 +2437,12 @@ have_op:
goto out;
}
break;
+ case OP_WRITE_ATOMIC:
+ if (!do_atomic_writes) {
+ log4(OP_WRITE_ATOMIC, offset, size, FL_SKIPPED);
+ goto out;
+ }
+ break;
}

switch (op) {
@@ -2385,6 +2472,11 @@ have_op:
dowrite(offset, size, 0);
break;

+ case OP_WRITE_ATOMIC:
+ TRIM_OFF_LEN(offset, size, maxfilelen);
+ dowrite(offset, size, RWF_ATOMIC);
+ break;
+
case OP_MAPREAD:
TRIM_OFF_LEN(offset, size, file_size);
domapread(offset, size);
@@ -2511,13 +2603,14 @@ void
usage(void)
{
fprintf(stdout, "usage: %s",
- "fsx [-dfhknqxyzBEFHIJKLORWXZ0]\n\
+ "fsx [-adfhknqxyzBEFHIJKLORWXZ0]\n\
[-b opnum] [-c Prob] [-g filldata] [-i logdev] [-j logid]\n\
[-l flen] [-m start:end] [-o oplen] [-p progressinterval]\n\
[-r readbdy] [-s style] [-t truncbdy] [-w writebdy]\n\
[-A|-U] [-D startingop] [-N numops] [-P dirpath] [-S seed]\n\
[--replay-ops=opsfile] [--record-ops[=opsfile]] [--duration=seconds]\n\
... fname\n\
+ -a: disable atomic writes\n\
-b opnum: beginning operation number (default 1)\n\
-c P: 1 in P chance of file close+open at each op (default infinity)\n\
-d: debug output for all operations\n\
@@ -3059,9 +3152,13 @@ main(int argc, char **argv)
setvbuf(stdout, (char *)0, _IOLBF, 0); /* line buffered stdout */

while ((ch = getopt_long(argc, argv,
- "0b:c:de:fg:hi:j:kl:m:no:p:qr:s:t:uw:xyABD:EFJKHzCILN:OP:RS:UWXZ",
+ "0ab:c:de:fg:hi:j:kl:m:no:p:qr:s:t:uw:xyABD:EFJKHzCILN:OP:RS:UWXZ",
longopts, NULL)) != EOF)
switch (ch) {
+ case 'a':
+ prt("main(): Atomic writes disabled\n");
+ do_atomic_writes = 0;
+ break;
case 'b':
simulatedopcount = getnum(optarg, &endp);
if (!quiet)
@@ -3475,6 +3572,8 @@ main(int argc, char **argv)
exchange_range_calls = test_exchange_range();
if (dontcache_io)
dontcache_io = test_dontcache_io();
+ if (do_atomic_writes)
+ do_atomic_writes = test_atomic_writes();

while (keep_running())
if (!test())
--
2.49.0