[PATCH v2 2/3] samples/vfs: Split out common code for new syscall APIs

[Sargun Dhillon <sargun@sargun.me>]

There are a bunch of helper functions which make using the new
mount APIs much easier. As we add examples of leveraging the
new APIs, it probably makes sense to promote code reuse.

Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kyle Anderson <kylea@netflix.com>
---
 samples/vfs/Makefile       |  2 +
 samples/vfs/test-fsmount.c | 86 +-------------------------------------
 samples/vfs/vfs-helper.c   | 43 +++++++++++++++++++
 samples/vfs/vfs-helper.h   | 55 ++++++++++++++++++++++++
 4 files changed, 101 insertions(+), 85 deletions(-)
 create mode 100644 samples/vfs/vfs-helper.c
 create mode 100644 samples/vfs/vfs-helper.h

diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
index 00b6824f9237..7f76875eaa70 100644
--- a/samples/vfs/Makefile
+++ b/samples/vfs/Makefile
@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
+test-fsmount-objs := test-fsmount.o vfs-helper.o
 userprogs := test-fsmount test-statx
+
 always-y := $(userprogs)
 
 userccflags += -I usr/include
diff --git a/samples/vfs/test-fsmount.c b/samples/vfs/test-fsmount.c
index 50f47b72e85f..36a4fa886200 100644
--- a/samples/vfs/test-fsmount.c
+++ b/samples/vfs/test-fsmount.c
@@ -14,91 +14,7 @@
 #include <sys/wait.h>
 #include <linux/mount.h>
 #include <linux/unistd.h>
-
-#define E(x) do { if ((x) == -1) { perror(#x); exit(1); } } while(0)
-
-static void check_messages(int fd)
-{
-	char buf[4096];
-	int err, n;
-
-	err = errno;
-
-	for (;;) {
-		n = read(fd, buf, sizeof(buf));
-		if (n < 0)
-			break;
-		n -= 2;
-
-		switch (buf[0]) {
-		case 'e':
-			fprintf(stderr, "Error: %*.*s\n", n, n, buf + 2);
-			break;
-		case 'w':
-			fprintf(stderr, "Warning: %*.*s\n", n, n, buf + 2);
-			break;
-		case 'i':
-			fprintf(stderr, "Info: %*.*s\n", n, n, buf + 2);
-			break;
-		}
-	}
-
-	errno = err;
-}
-
-static __attribute__((noreturn))
-void mount_error(int fd, const char *s)
-{
-	check_messages(fd);
-	fprintf(stderr, "%s: %m\n", s);
-	exit(1);
-}
-
-/* Hope -1 isn't a syscall */
-#ifndef __NR_fsopen
-#define __NR_fsopen -1
-#endif
-#ifndef __NR_fsmount
-#define __NR_fsmount -1
-#endif
-#ifndef __NR_fsconfig
-#define __NR_fsconfig -1
-#endif
-#ifndef __NR_move_mount
-#define __NR_move_mount -1
-#endif
-
-
-static inline int fsopen(const char *fs_name, unsigned int flags)
-{
-	return syscall(__NR_fsopen, fs_name, flags);
-}
-
-static inline int fsmount(int fsfd, unsigned int flags, unsigned int ms_flags)
-{
-	return syscall(__NR_fsmount, fsfd, flags, ms_flags);
-}
-
-static inline int fsconfig(int fsfd, unsigned int cmd,
-			   const char *key, const void *val, int aux)
-{
-	return syscall(__NR_fsconfig, fsfd, cmd, key, val, aux);
-}
-
-static inline int move_mount(int from_dfd, const char *from_pathname,
-			     int to_dfd, const char *to_pathname,
-			     unsigned int flags)
-{
-	return syscall(__NR_move_mount,
-		       from_dfd, from_pathname,
-		       to_dfd, to_pathname, flags);
-}
-
-#define E_fsconfig(fd, cmd, key, val, aux)				\
-	do {								\
-		if (fsconfig(fd, cmd, key, val, aux) == -1)		\
-			mount_error(fd, key ?: "create");		\
-	} while (0)
+#include "vfs-helper.h"
 
 int main(int argc, char *argv[])
 {
diff --git a/samples/vfs/vfs-helper.c b/samples/vfs/vfs-helper.c
new file mode 100644
index 000000000000..bae2bc03c923
--- /dev/null
+++ b/samples/vfs/vfs-helper.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include "vfs-helper.h"
+
+void check_messages(int fd)
+{
+	char buf[4096];
+	int err, n;
+
+	err = errno;
+
+	for (;;) {
+		n = read(fd, buf, sizeof(buf));
+		if (n < 0)
+			break;
+		n -= 2;
+
+		switch (buf[0]) {
+		case 'e':
+			fprintf(stderr, "Error: %*.*s\n", n, n, buf + 2);
+			break;
+		case 'w':
+			fprintf(stderr, "Warning: %*.*s\n", n, n, buf + 2);
+			break;
+		case 'i':
+			fprintf(stderr, "Info: %*.*s\n", n, n, buf + 2);
+			break;
+		}
+	}
+
+	errno = err;
+}
+
+__attribute__((noreturn))
+void mount_error(int fd, const char *s)
+{
+	check_messages(fd);
+	fprintf(stderr, "%s: %m\n", s);
+	exit(1);
+}
\ No newline at end of file
diff --git a/samples/vfs/vfs-helper.h b/samples/vfs/vfs-helper.h
new file mode 100644
index 000000000000..be460ab48247
--- /dev/null
+++ b/samples/vfs/vfs-helper.h
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/unistd.h>
+#include <linux/mount.h>
+#include <sys/syscall.h>
+
+#define E(x) do { if ((x) == -1) { perror(#x); exit(1); } } while(0)
+
+/* Hope -1 isn't a syscall */
+#ifndef __NR_fsopen
+#define __NR_fsopen -1
+#endif
+#ifndef __NR_fsmount
+#define __NR_fsmount -1
+#endif
+#ifndef __NR_fsconfig
+#define __NR_fsconfig -1
+#endif
+#ifndef __NR_move_mount
+#define __NR_move_mount -1
+#endif
+
+#define E_fsconfig(fd, cmd, key, val, aux)				\
+	do {								\
+		if (fsconfig(fd, cmd, key, val, aux) == -1)		\
+			mount_error(fd, key ?: "create");		\
+	} while (0)
+
+static inline int fsopen(const char *fs_name, unsigned int flags)
+{
+	return syscall(__NR_fsopen, fs_name, flags);
+}
+
+static inline int fsmount(int fsfd, unsigned int flags, unsigned int ms_flags)
+{
+	return syscall(__NR_fsmount, fsfd, flags, ms_flags);
+}
+
+static inline int fsconfig(int fsfd, unsigned int cmd,
+			   const char *key, const void *val, int aux)
+{
+	return syscall(__NR_fsconfig, fsfd, cmd, key, val, aux);
+}
+
+static inline int move_mount(int from_dfd, const char *from_pathname,
+			     int to_dfd, const char *to_pathname,
+			     unsigned int flags)
+{
+	return syscall(__NR_move_mount,
+		       from_dfd, from_pathname,
+		       to_dfd, to_pathname, flags);
+}
+
+__attribute__((noreturn))
+void mount_error(int fd, const char *s);
+void check_messages(int fd);
-- 
2.25.1