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103 changes: 92 additions & 11 deletions lib/mount_fsmount.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,87 @@
#include <sys/mount.h>
#include <sys/syscall.h>

#ifdef NEED_NEW_MOUNT_API_SYSCALL_WRAPPERS
/*
* Kernel supports the new mount API (fsopen/fsconfig/fsmount/move_mount)
* but libc doesn't provide the wrapper functions yet (e.g. glibc added
* these only in 2.36) - call the syscalls directly. Numbers are
* identical across x86_64, i386, arm and arm64. fuse_-prefixed so the
* fallback never clashes with a libc extern declaration; where libc has
* them the #else aliases map straight to the libc wrappers.
*/
#ifndef __NR_fsopen
#define __NR_fsopen 430
#endif
#ifndef __NR_fsconfig
#define __NR_fsconfig 431
#endif
#ifndef __NR_fsmount
#define __NR_fsmount 432
#endif
#ifndef __NR_move_mount
#define __NR_move_mount 429
#endif

static inline int fuse_fsopen(const char *fsname, unsigned int flags)
{
return syscall(__NR_fsopen, fsname, flags);
}

static inline int fuse_fsconfig(int fd, unsigned int cmd, const char *key,
const void *value, int aux)
{
return syscall(__NR_fsconfig, fd, cmd, key, value, aux);
}

static inline int fuse_fsmount(int fd, unsigned int flags, unsigned int ms_flags)
{
return syscall(__NR_fsmount, fd, flags, ms_flags);
}

static inline int fuse_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);
}
#else
#define fuse_fsopen fsopen
#define fuse_fsconfig fsconfig
#define fuse_fsmount fsmount
#define fuse_move_mount move_mount
#endif /* NEED_NEW_MOUNT_API_SYSCALL_WRAPPERS */

/*
* New mount API constants come from <linux/mount.h>. Define the ones an
* older or partial uapi header omits so this file still builds - values are
* the kernel uapi definitions. FSCONFIG_* are an enum there, so these guards
* fire only when a name is genuinely absent; <linux/mount.h> is already
* included via mount_i_linux.h, so a fallback macro cannot clash with it.
*/
#ifndef FSOPEN_CLOEXEC
#define FSOPEN_CLOEXEC 0x00000001
#endif
#ifndef FSMOUNT_CLOEXEC
#define FSMOUNT_CLOEXEC 0x00000001
#endif
#ifndef MOVE_MOUNT_F_EMPTY_PATH
#define MOVE_MOUNT_F_EMPTY_PATH 0x00000004
#endif
#ifndef MOVE_MOUNT_T_EMPTY_PATH
#define MOVE_MOUNT_T_EMPTY_PATH 0x00000040
#endif
#ifndef FSCONFIG_SET_FLAG
#define FSCONFIG_SET_FLAG 0
#endif
#ifndef FSCONFIG_SET_STRING
#define FSCONFIG_SET_STRING 1
#endif
#ifndef FSCONFIG_CMD_CREATE
#define FSCONFIG_CMD_CREATE 6
#endif

/*
* Mount attribute flags for fsmount() - from linux/mount.h
* This file is only compiled conditionally when support for the new
Expand Down Expand Up @@ -107,7 +188,7 @@ int set_fsconfig_ms_flags(int fsfd, unsigned long *ms_flags)
if (!(flags & mount_flags[i].flag))
continue;

ret = fsconfig(fsfd, FSCONFIG_SET_FLAG, mount_flags[i].opt, NULL, 0);
ret = fuse_fsconfig(fsfd, FSCONFIG_SET_FLAG, mount_flags[i].opt, NULL, 0);
if (ret) {
int save_errno = errno;

Expand Down Expand Up @@ -137,7 +218,7 @@ int apply_fsconfig_opt_fd(int fsfd, const char *value)
int res;

/* The fd parameter is a u32 value, not a file descriptor to pass */
res = fsconfig(fsfd, FSCONFIG_SET_STRING, "fd", value, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_SET_STRING, "fd", value, 0);
if (res == -1) {
int save_errno = errno;

Expand All @@ -153,7 +234,7 @@ int apply_fsconfig_opt_string(int fsfd, const char *key, const char *value)
{
int res, save_errno;

res = fsconfig(fsfd, FSCONFIG_SET_STRING, key, value, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_SET_STRING, key, value, 0);
save_errno = errno;
if (res == -1) {
fuse_log(FUSE_LOG_ERR, "fuse: fsconfig SET_STRING %s=%s failed: ",
Expand All @@ -169,7 +250,7 @@ int fuse_fsopen_base_type(int blkdev)
const char *type = blkdev ? "fuseblk" : "fuse";
int fsfd;

fsfd = fsopen(type, FSOPEN_CLOEXEC);
fsfd = fuse_fsopen(type, FSOPEN_CLOEXEC);
if (fsfd == -1)
return -errno;
return fsfd;
Expand All @@ -179,7 +260,7 @@ int fuse_fsconfig_subtype(int fsfd, const char *subtype)
{
int res;

res = fsconfig(fsfd, FSCONFIG_SET_STRING, "subtype", subtype, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_SET_STRING, "subtype", subtype, 0);
if (res == -1) {
int save_errno = errno;

Expand Down Expand Up @@ -213,7 +294,7 @@ static int apply_opt_flag(int fsfd, const char *opt)
{
int res;

res = fsconfig(fsfd, FSCONFIG_SET_FLAG, opt, NULL, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_SET_FLAG, opt, NULL, 0);
if (res == -1) {
int save_errno = errno;

Expand Down Expand Up @@ -450,7 +531,7 @@ int fuse_kern_fsmount(const char *mnt, int dest_mnt_fd, unsigned long flags,
}

/* Configure source */
res = fsconfig(fsfd, FSCONFIG_SET_STRING, "source", source, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_SET_STRING, "source", source, 0);
if (res == -1) {
err = -errno;
log_fsconfig_kmsg(fsfd);
Expand All @@ -475,7 +556,7 @@ int fuse_kern_fsmount(const char *mnt, int dest_mnt_fd, unsigned long flags,
}

/* Create the filesystem instance */
res = fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
res = fuse_fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
if (res == -1) {
err = -errno;
log_fsconfig_kmsg(fsfd);
Expand All @@ -493,7 +574,7 @@ int fuse_kern_fsmount(const char *mnt, int dest_mnt_fd, unsigned long flags,
}

/* Create mount object with mount attributes */
mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, mount_attrs);
mountfd = fuse_fsmount(fsfd, FSMOUNT_CLOEXEC, mount_attrs);
if (mountfd == -1) {
err = -errno;
log_fsconfig_kmsg(fsfd);
Expand All @@ -506,11 +587,11 @@ int fuse_kern_fsmount(const char *mnt, int dest_mnt_fd, unsigned long flags,
fsfd = -1;

if (dest_mnt_fd >= 0)
res = move_mount(mountfd, "", dest_mnt_fd, "",
res = fuse_move_mount(mountfd, "", dest_mnt_fd, "",
MOVE_MOUNT_F_EMPTY_PATH |
MOVE_MOUNT_T_EMPTY_PATH);
else
res = move_mount(mountfd, "", AT_FDCWD, mnt,
res = fuse_move_mount(mountfd, "", AT_FDCWD, mnt,
MOVE_MOUNT_F_EMPTY_PATH);
if (res == -1) {
err = -errno;
Expand Down
71 changes: 56 additions & 15 deletions meson.build
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -131,21 +131,6 @@ special_funcs = {
}
}
''',
'new_mount_api': '''
#define _GNU_SOURCE
#include <sys/mount.h>
#include <linux/mount.h>
#include <unistd.h>
#include <fcntl.h>

int main(void) {
int fsfd = fsopen("fuse", FSOPEN_CLOEXEC);
int res = fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "test", 0);
int mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
res = move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
return 0;
}
''',
'systemd_headers': '''
#include <systemd/sd-daemon.h>

Expand All @@ -161,6 +146,62 @@ foreach name, code : special_funcs
name: name + ' check'))
endforeach

# New Linux mount API (fsopen/fsconfig/fsmount/move_mount): the kernel
# syscalls landed in 5.2, but libc wrapper functions can lag behind (e.g.
# glibc added them only in 2.36). Test kernel header support and libc
# wrapper support separately, so the direct syscall() fallback wrappers
# in mount_i_linux.h are used whenever libc lacks them - regardless of
# which libc or distro that is. The two code snippets and the arg list
# are named so test/meson.build can reuse them verbatim against fixture
# headers, instead of duplicating the checks.
mount_api_headers_check_code = '''
#include <linux/mount.h>
int main(void) {
int x = FSOPEN_CLOEXEC | FSMOUNT_CLOEXEC | MOVE_MOUNT_F_EMPTY_PATH;
int y = FSCONFIG_SET_STRING | FSCONFIG_CMD_CREATE;
int z = MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV |
MOUNT_ATTR_NOEXEC | MOUNT_ATTR_NOATIME;
return x + y + z;
}
'''

mount_api_libc_check_code = '''
#define _GNU_SOURCE
#include <sys/mount.h>
#include <linux/mount.h>
#include <unistd.h>
#include <fcntl.h>

int main(void) {
int fsfd = fsopen("fuse", FSOPEN_CLOEXEC);
int res = fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "test", 0);
int mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
res = move_mount(mntfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
return 0;
}
'''

# -Werror=implicit-function-declaration: without it, a missing
# declaration only warns on some compilers, and the link can still
# silently succeed against a same-named symbol the libc happens to
# export - which would defeat the point of testing for the wrapper
# functions' declared presence.
mount_api_check_args = args_default + [ '-Werror=implicit-function-declaration' ]

have_new_mount_api_headers = cc.compiles(mount_api_headers_check_code,
args: mount_api_check_args,
name: 'new mount API headers check')

have_new_mount_api_libc_funcs = cc.links(mount_api_libc_check_code,
args: mount_api_check_args,
name: 'new mount API libc wrapper check')

private_cfg.set('HAVE_NEW_MOUNT_API', have_new_mount_api_headers)
if have_new_mount_api_headers and not have_new_mount_api_libc_funcs
private_cfg.set('NEED_NEW_MOUNT_API_SYSCALL_WRAPPERS', true)
message('libc lacks new mount API wrapper functions, using direct syscalls')
endif

# Headers checks
test_headers = [ 'sys/xattr.h', 'linux/limits.h' ]
foreach header : test_headers
Expand Down
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