FreeBSD: Add posix_fadvise(POSIX_FADV_WILLNEED) support

As commit 320f0c6 did for Linux, connect POSIX_FADV_WILLNEED
up to dmu_prefetch() on FreeBSD.

While there, fix portability problems in tests/functional/fadvise.

1.  Instead of relying on the numerical values of POSIX_FADV_XXX macros,
    accept macro names as arguments to the file_fadvise program.  (The
    numbers happen to match on Linux and FreeBSD, but future systems may
    vary and it seems a little strange/raw to count on that.)

2.  For implementation reasons, SEQUENTIAL doesn't reach ZFS via FreeBSD
    VFS currently (perhaps something that should be investigated in
    FreeBSD).  Since on Linux we're treating SEQUENTIAL and WILLNEED the
    same, it doesn't really matter which one we use, so switch the test
    over to WILLNEED exercise the new prefetch code on both OSes the
    same way.

Reviewed-by: Mateusz Guzik <mjg@FreeBSD.org>
Reviewed-by: Fedor Uporov <fuporov.vstack@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Thomas Munro <tmunro@FreeBSD.org>
Co-authored-by: Alexander Motin <mav@FreeBSD.org>
Closes #17379

tests/zfs-tests/cmd/Makefile.am

@@ -140,7 +140,7 @@ scripts_zfs_tests_bin_PROGRAMS  += %D%/read_dos_attributes %D%/write_dos_attribu
 
 scripts_zfs_tests_bin_PROGRAMS += %D%/randfree_file
 %C%_randfree_file_SOURCES       = %D%/file/randfree_file.c
+endif
 
 scripts_zfs_tests_bin_PROGRAMS += %D%/file_fadvise
 %C%_file_fadvise_SOURCES  = %D%/file/file_fadvise.c
-endif

tests/zfs-tests/cmd/file/file_fadvise.c

@@ -44,21 +44,41 @@ static void
 usage(void)
 {
 	(void) fprintf(stderr,
-	    "usage: %s -f filename -a advise \n", execname);
+	    "usage: %s -f filename -a advice \n", execname);
 }
 
+typedef struct advice_name {
+	const char *name;
+	int value;
+} advice_name;
+
+static const struct advice_name table[] = {
+#define	ADV(name) {#name, name}
+	ADV(POSIX_FADV_NORMAL),
+	ADV(POSIX_FADV_RANDOM),
+	ADV(POSIX_FADV_SEQUENTIAL),
+	ADV(POSIX_FADV_WILLNEED),
+	ADV(POSIX_FADV_DONTNEED),
+	ADV(POSIX_FADV_NOREUSE),
+	{NULL}
+};
+
 int
 main(int argc, char *argv[])
 {
 	char *filename = NULL;
-	int advise = 0;
+	int advice = POSIX_FADV_NORMAL;
 	int fd, ch;
 	int	err = 0;
 
 	while ((ch = getopt(argc, argv, "a:f:")) != EOF) {
 		switch (ch) {
 		case 'a':
-			advise = atoll(optarg);
+			advice = -1;
+			for (const advice_name *p = table; p->name; ++p) {
+				if (strcmp(p->name, optarg) == 0)
+					advice = p->value;
+			}
 			break;
 		case 'f':
 			filename = optarg;
@@ -75,8 +95,8 @@ main(int argc, char *argv[])
 		err++;
 	}
 
-	if (advise < POSIX_FADV_NORMAL || advise > POSIX_FADV_NOREUSE) {
-		(void) printf("advise is invalid\n");
+	if (advice == -1) {
+		(void) printf("advice is invalid\n");
 		err++;
 	}
 
@@ -90,7 +110,7 @@ main(int argc, char *argv[])
 		return (1);
 	}
 
-	if (posix_fadvise(fd, 0, 0, advise) != 0) {
+	if (posix_fadvise(fd, 0, 0, advice) != 0) {
 		perror("posix_fadvise");
 		close(fd);
 		return (1);

tests/zfs-tests/tests/Makefile.am

@@ -1526,7 +1526,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/exec/exec_002_neg.ksh \
 	functional/exec/setup.ksh \
 	functional/fadvise/cleanup.ksh \
-	functional/fadvise/fadvise_sequential.ksh \
+	functional/fadvise/fadvise_willneed.ksh \
 	functional/fadvise/setup.ksh \
 	functional/failmode/cleanup.ksh \
 	functional/failmode/failmode_dmu_tx_wait.ksh \

tests/zfs-tests/tests/functional/fadvise/fadvise_willneed.ksh

@@ -42,7 +42,7 @@
 #
 
 # NOTE: if HAVE_FILE_FADVISE is not defined former data_size
-# should less or eaqul to latter one
+# should less or equal to latter one
 
 verify_runnable "global"
 
@@ -66,7 +66,7 @@ sync_pool $TESTPOOL
 
 data_size1=$(kstat arcstats.data_size)
 
-log_must file_fadvise -f $FILE -a 2
+log_must file_fadvise -f $FILE -a POSIX_FADV_WILLNEED
 sleep 10
 
 data_size2=$(kstat arcstats.data_size)