[PATCH 2/2] fsx: add support for RWF_DONTCACHE

[Jens Axboe <axboe@kernel.dk>]

Using RWF_DONTCACHE tells the kernel that any page cache instantiated
by this operation should get pruned once the operation completes. If
data is in cache prior to the operation it will remain there.

Add ops for testing both the read and write side of this. At startup,
kernel support for this feature is probed. If support isn't available,
uncached/dontcache IO is performed as regular buffered IO. If -Z is
used to turn on O_DIRECT, then uncached/dontcache IO isn't performed.
Defaults to on if available, and adds a -T parameter to turn it off.

See the kernel posting adding support:

https://lore.kernel.org/linux-fsdevel/20241220154831.1086649-1-axboe@kernel.dk/

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 ltp/fsx.c | 114 ++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 76 insertions(+), 38 deletions(-)

diff --git a/ltp/fsx.c b/ltp/fsx.c
index 41933354328a..9efd2f5c86d1 100644
--- a/ltp/fsx.c
+++ b/ltp/fsx.c
@@ -43,6 +43,10 @@
 # define MAP_FILE 0
 #endif
 
+#ifndef RWF_DONTCACHE
+#define RWF_DONTCACHE	0x80
+#endif
+
 #define NUMPRINTCOLUMNS 32	/* # columns of data to print on each line */
 
 /* Operation flags (bitmask) */
@@ -101,7 +105,9 @@ int			logcount = 0;	/* total ops */
 enum {
 	/* common operations */
 	OP_READ = 0,
+	OP_READ_DONTCACHE,
 	OP_WRITE,
+	OP_WRITE_DONTCACHE,
 	OP_MAPREAD,
 	OP_MAPWRITE,
 	OP_MAX_LITE,
@@ -190,15 +196,16 @@ int	o_direct;			/* -Z */
 int	aio = 0;
 int	uring = 0;
 int	mark_nr = 0;
+int	dontcache_io = 1;
 
 int page_size;
 int page_mask;
 int mmap_mask;
-int fsx_rw(int rw, int fd, char *buf, unsigned len, unsigned offset);
+int fsx_rw(int rw, int fd, char *buf, unsigned len, unsigned offset, int flags);
 #define READ 0
 #define WRITE 1
-#define fsxread(a,b,c,d)	fsx_rw(READ, a,b,c,d)
-#define fsxwrite(a,b,c,d)	fsx_rw(WRITE, a,b,c,d)
+#define fsxread(a,b,c,d,f)	fsx_rw(READ, a,b,c,d,f)
+#define fsxwrite(a,b,c,d,f)	fsx_rw(WRITE, a,b,c,d,f)
 
 struct timespec deadline;
 
@@ -266,7 +273,9 @@ prterr(const char *prefix)
 
 static const char *op_names[] = {
 	[OP_READ] = "read",
+	[OP_READ_DONTCACHE] = "read_dontcache",
 	[OP_WRITE] = "write",
+	[OP_WRITE_DONTCACHE] = "write_dontcache",
 	[OP_MAPREAD] = "mapread",
 	[OP_MAPWRITE] = "mapwrite",
 	[OP_TRUNCATE] = "truncate",
@@ -393,12 +402,14 @@ logdump(void)
 				prt("\t******WWWW");
 			break;
 		case OP_READ:
+		case OP_READ_DONTCACHE:
 			prt("READ     0x%x thru 0x%x\t(0x%x bytes)",
 			    lp->args[0], lp->args[0] + lp->args[1] - 1,
 			    lp->args[1]);
 			if (overlap)
 				prt("\t***RRRR***");
 			break;
+		case OP_WRITE_DONTCACHE:
 		case OP_WRITE:
 			prt("WRITE    0x%x thru 0x%x\t(0x%x bytes)",
 			    lp->args[0], lp->args[0] + lp->args[1] - 1,
@@ -784,9 +795,8 @@ doflush(unsigned offset, unsigned size)
 }
 
 void
-doread(unsigned offset, unsigned size)
+doread(unsigned offset, unsigned size, int flags)
 {
-	off_t ret;
 	unsigned iret;
 
 	offset -= offset % readbdy;
@@ -818,12 +828,7 @@ doread(unsigned offset, unsigned size)
 			(monitorend == -1 || offset <= monitorend))))))
 		prt("%lld read\t0x%x thru\t0x%x\t(0x%x bytes)\n", testcalls,
 		    offset, offset + size - 1, size);
-	ret = lseek(fd, (off_t)offset, SEEK_SET);
-	if (ret == (off_t)-1) {
-		prterr("doread: lseek");
-		report_failure(140);
-	}
-	iret = fsxread(fd, temp_buf, size, offset);
+	iret = fsxread(fd, temp_buf, size, offset, flags);
 	if (iret != size) {
 		if (iret == -1)
 			prterr("doread: read");
@@ -870,7 +875,6 @@ check_contents(void)
 	unsigned map_offset;
 	unsigned map_size;
 	char *p;
-	off_t ret;
 	unsigned iret;
 
 	if (!check_buf) {
@@ -885,13 +889,7 @@ check_contents(void)
 	if (size == 0)
 		return;
 
-	ret = lseek(fd, (off_t)offset, SEEK_SET);
-	if (ret == (off_t)-1) {
-		prterr("doread: lseek");
-		report_failure(140);
-	}
-
-	iret = fsxread(fd, check_buf, size, offset);
+	iret = fsxread(fd, check_buf, size, offset, 0);
 	if (iret != size) {
 		if (iret == -1)
 			prterr("check_contents: read");
@@ -1064,9 +1062,8 @@ update_file_size(unsigned offset, unsigned size)
 }
 
 void
-dowrite(unsigned offset, unsigned size)
+dowrite(unsigned offset, unsigned size, int flags)
 {
-	off_t ret;
 	unsigned iret;
 
 	offset -= offset % writebdy;
@@ -1099,14 +1096,9 @@ dowrite(unsigned offset, unsigned size)
 		       (monitorstart == -1 ||
 			(offset + size > monitorstart &&
 			(monitorend == -1 || offset <= monitorend))))))
-		prt("%lld write\t0x%x thru\t0x%x\t(0x%x bytes)\n", testcalls,
-		    offset, offset + size - 1, size);
-	ret = lseek(fd, (off_t)offset, SEEK_SET);
-	if (ret == (off_t)-1) {
-		prterr("dowrite: lseek");
-		report_failure(150);
-	}
-	iret = fsxwrite(fd, good_buf + offset, size, offset);
+		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);
+	iret = fsxwrite(fd, good_buf + offset, size, offset, flags);
 	if (iret != size) {
 		if (iret == -1)
 			prterr("dowrite: write");
@@ -1954,6 +1946,26 @@ do_preallocate(unsigned offset, unsigned length, int keep_size, int unshare)
 }
 #endif
 
+int
+test_dontcache_io(void)
+{
+	char buf[4096];
+	struct iovec iov = { .iov_base = buf, .iov_len = sizeof(buf) };
+	int ret, e;
+
+	ret = preadv2(fd, &iov, 1, 0, RWF_DONTCACHE);
+	e = ret < 0 ? errno : 0;
+	if (e == EOPNOTSUPP) {
+		if (!quiet)
+			fprintf(stderr,
+				"main: filesystem does not support "
+				"dontcache IO, disabling!\n");
+		return 0;
+	}
+
+	return 1;
+}
+
 void
 writefileimage()
 {
@@ -2337,12 +2349,28 @@ have_op:
 	switch (op) {
 	case OP_READ:
 		TRIM_OFF_LEN(offset, size, file_size);
-		doread(offset, size);
+		doread(offset, size, 0);
+		break;
+
+	case OP_READ_DONTCACHE:
+		TRIM_OFF_LEN(offset, size, file_size);
+		if (dontcache_io)
+			doread(offset, size, RWF_DONTCACHE);
+		else
+			doread(offset, size, 0);
 		break;
 
 	case OP_WRITE:
 		TRIM_OFF_LEN(offset, size, maxfilelen);
-		dowrite(offset, size);
+		dowrite(offset, size, 0);
+		break;
+
+	case OP_WRITE_DONTCACHE:
+		TRIM_OFF_LEN(offset, size, maxfilelen);
+		if (dontcache_io)
+			dowrite(offset, size, RWF_DONTCACHE);
+		else
+			dowrite(offset, size, 0);
 		break;
 
 	case OP_MAPREAD:
@@ -2538,6 +2566,7 @@ usage(void)
 "	-0: Do not use exchange range calls\n"
 #endif
 "	-K: Do not use keep size\n\
+	-T: Do not use dontcache IO\n\
 	-L: fsxLite - no file creations & no file size changes\n\
 	-N numops: total # operations to do (default infinity)\n\
 	-O: use oplen (see -o flag) for every op (default random)\n\
@@ -2546,7 +2575,7 @@ usage(void)
 	-S seed: for random # generator (default 1) 0 gets timestamp\n\
 	-W: mapped write operations DISabled\n\
 	-X: Read file and compare to good buffer after every operation\n\
-	-Z: O_DIRECT (use -R, -W, -r and -w too)\n\
+	-Z: O_DIRECT (use -R, -W, -r and -w too, excludes dontcache IO)\n\
 	--replay-ops=opsfile: replay ops from recorded .fsxops file\n\
 	--record-ops[=opsfile]: dump ops file also on success. optionally specify ops file name\n\
 	--duration=seconds: ignore any -N setting and run for this many seconds\n\
@@ -2702,7 +2731,7 @@ uring_setup()
 }
 
 int
-uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
+uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset, int flags)
 {
 	struct io_uring_sqe     *sqe;
 	struct io_uring_cqe     *cqe;
@@ -2733,6 +2762,7 @@ uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
 		} else {
 			io_uring_prep_writev(sqe, fd, &iovec, 1, o);
 		}
+		sqe->rw_flags = flags;
 
 		ret = io_uring_submit_and_wait(&ring, 1);
 		if (ret != 1) {
@@ -2781,7 +2811,7 @@ uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
 }
 #else
 int
-uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
+uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset, int flags)
 {
 	fprintf(stderr, "io_rw: need IO_URING support!\n");
 	exit(111);
@@ -2789,19 +2819,21 @@ uring_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
 #endif
 
 int
-fsx_rw(int rw, int fd, char *buf, unsigned len, unsigned offset)
+fsx_rw(int rw, int fd, char *buf, unsigned len, unsigned offset, int flags)
 {
 	int ret;
 
 	if (aio) {
 		ret = aio_rw(rw, fd, buf, len, offset);
 	} else if (uring) {
-		ret = uring_rw(rw, fd, buf, len, offset);
+		ret = uring_rw(rw, fd, buf, len, offset, flags);
 	} else {
+		struct iovec iov = { .iov_base = buf, .iov_len = len };
+
 		if (rw == READ)
-			ret = read(fd, buf, len);
+			ret = preadv2(fd, &iov, 1, offset, flags);
 		else
-			ret = write(fd, buf, len);
+			ret = pwritev2(fd, &iov, 1, offset, flags);
 	}
 	return ret;
 }
@@ -3065,6 +3097,9 @@ main(int argc, char **argv)
 			if (seed < 0)
 				usage();
 			break;
+		case 'T':
+			dontcache_io = 0;
+			break;
 		case 'W':
 		        mapped_writes = 0;
 			if (!quiet)
@@ -3076,6 +3111,7 @@ main(int argc, char **argv)
 		case 'Z':
 			o_direct = O_DIRECT;
 			o_flags |= O_DIRECT;
+			dontcache_io = 0;
 			break;
 		case 254:  /* --duration */
 			if (!optarg) {
@@ -3293,6 +3329,8 @@ main(int argc, char **argv)
 		copy_range_calls = test_copy_range();
 	if (exchange_range_calls)
 		exchange_range_calls = test_exchange_range();
+	if (dontcache_io)
+		dontcache_io = test_dontcache_io();
 
 	while (keep_running())
 		if (!test())
-- 
2.47.1