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Commit f1b5618e authored by David Howells's avatar David Howells Committed by Al Viro
Browse files

vfs: Add a sample program for the new mount API 



Add a sample program to demonstrate fsopen/fsmount/move_mount to mount
something.

To make it compile on all arches, irrespective of whether or not syscall
numbers are assigned, define the syscall number to -1 if it isn't to cause
the kernel to return -ENOSYS.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent cf3cba4a

samples/Kconfig

+5 −4
Original line number Diff line number Diff line
@@ -154,10 +154,11 @@ config SAMPLE_ANDROID_BINDERFS 
	  Builds a sample program to illustrate the use of the Android binderfs

	  filesystem.



config SAMPLE_STATX

	bool "Build example extended-stat using code"

	depends on BROKEN

config SAMPLE_VFS

	bool "Build example programs that use new VFS system calls"

	help

	  Build example userspace program to use the new extended-stat syscall.

	  Build example userspace programs that use new VFS system calls such

	  as mount API and statx().  Note that this is restricted to the x86

	  arch whilst it accesses system calls that aren't yet in all arches.



endif # SAMPLES

samples/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -3,4 +3,4 @@ 
obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ trace_events/ livepatch/ \

			   hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \

			   configfs/ connector/ v4l/ trace_printk/ \

			   vfio-mdev/ statx/ qmi/ binderfs/
 
			   vfio-mdev/ vfs/ qmi/ binderfs/

samples/statx/Makefile→samples/vfs/Makefile

+4 −1
Original line number Diff line number Diff line 
# List of programs to build

hostprogs-$(CONFIG_SAMPLE_STATX) := test-statx

hostprogs-$(CONFIG_SAMPLE_VFS) := \

	test-fsmount \

	test-statx



# Tell kbuild to always build the programs

always := $(hostprogs-y)



HOSTCFLAGS_test-fsmount.o += -I$(objtree)/usr/include

HOSTCFLAGS_test-statx.o += -I$(objtree)/usr/include

samples/vfs/test-fsmount.c

0 → 100644
+133 −0
Original line number Diff line number Diff line 
/* fd-based mount test.

 *

 * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.

 * Written by David Howells (dhowells@redhat.com)

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public Licence

 * as published by the Free Software Foundation; either version

 * 2 of the Licence, or (at your option) any later version.

 */



#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <errno.h>

#include <fcntl.h>

#include <sys/prctl.h>

#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)



int main(int argc, char *argv[])

{

	int fsfd, mfd;



	/* Mount a publically available AFS filesystem */

	fsfd = fsopen("afs", 0);

	if (fsfd == -1) {

		perror("fsopen");

		exit(1);

	}



	E_fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "#grand.central.org:root.cell.", 0);

	E_fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);



	mfd = fsmount(fsfd, 0, MOUNT_ATTR_RDONLY);

	if (mfd < 0)

		mount_error(fsfd, "fsmount");

	E(close(fsfd));



	if (move_mount(mfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH) < 0) {

		perror("move_mount");

		exit(1);

	}



	E(close(mfd));

	exit(0);

}

samples/statx/test-statx.c→samples/vfs/test-statx.c

+10 −1
Original line number Diff line number Diff line
@@ -25,13 +25,21 @@ 
#include <sys/types.h>

#include <linux/stat.h>

#include <linux/fcntl.h>

#define statx foo

#define statx_timestamp foo_timestamp

#include <sys/stat.h>

#undef statx

#undef statx_timestamp



#define AT_STATX_SYNC_TYPE	0x6000

#define AT_STATX_SYNC_AS_STAT	0x0000

#define AT_STATX_FORCE_SYNC	0x2000

#define AT_STATX_DONT_SYNC	0x4000



#ifndef __NR_statx

#define __NR_statx -1

#endif



static __attribute__((unused))

ssize_t statx(int dfd, const char *filename, unsigned flags,

	      unsigned int mask, struct statx *buffer)
@@ -157,7 +165,8 @@ static void dump_statx(struct statx *stx) 
			"?dai?c??"	/*  7- 0	0x00000000-000000ff */

			;



		printf("Attributes: %016llx (", stx->stx_attributes);

		printf("Attributes: %016llx (",

		       (unsigned long long)stx->stx_attributes);

		for (byte = 64 - 8; byte >= 0; byte -= 8) {

			bits = stx->stx_attributes >> byte;

			mbits = stx->stx_attributes_mask >> byte;