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linux-user: implement fsmount(2) series of syscalls

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This series of syscalls replaces the old mount(2) syscall with a series
of syscalls that operates around a filesystem context. This series of
syscalls is available since Linux 5.2 and glibc 2.36+.

Their users include systemd since v259 and libmount from util-linux, and
possibly other widely used projects.

Preliminary checks are implemented to ensure the validity of the
interface.

v2: Add syscall wrappers in case the build machine does not
support the fsmount() syscalls. (added by Helge Deller)

Signed-off-by: Xinhui Yang <cyan@cyano.uk>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Xinhui Yang 2026-05-29 14:53:20 +08:00 • committed by Helge Deller
parent 29c042c6e9
commit 767c32fe69
1 changed files with 104 additions and 0 deletions
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104
linux-user/syscall.c
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@ -9713,6 +9713,19 @@ _syscall5(int, sys_move_mount, int, __from_dfd, const char *, __from_pathname,
int, __to_dfd, const char *, __to_pathname, unsigned int, flag)
#endif
#if defined(TARGET_NR_fsopen) && defined(NR_fsopen)
#define __NR_sys_fsopen __NR_fsopen
_syscall2(int, sys_fsopen, const char *, fs_name, unsigned int, flags);
#define __NR_sys_fsconfig __NR_fsconfig
_syscall5(int, sys_fsconfig, int, fs_fd, unsigned int, cmd, const char *, key,
const void *, value, int, aux)
#define __NR_sys_fsmount __NR_fsmount
_syscall3(int, sys_fsmount, int, fs_fd, unsigned int, flags,
unsigned int, ms_flags)
#define __NR_sys_fspick __NR_fspick
_syscall3(int, sys_fspick, int, dfd, const char *, path, unsigned int, flags)
#endif
/* This is an internal helper for do_syscall so that it is easier
* to have a single return point, so that actions, such as logging
* of syscall results, can be performed.
@ -14412,6 +14425,97 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
return do_map_shadow_stack(cpu_env, arg1, arg2, arg3);
#endif
#if defined(TARGET_NR_fsopen) && defined(NR_fsopen)
case TARGET_NR_fsopen:
{
p = lock_user_string(arg1);
if (!p) {
return -TARGET_EFAULT;
}
ret = get_errno(sys_fsopen(p, arg2));
unlock_user(p, arg1, 0);
}
return ret;
case TARGET_NR_fsconfig:
{
/*
* fsconfig(int, int, char *, void *, int)
* NOTE: p4 is nullable and its type might not be a string.
*/
void *p3, *p4;
int cmd = (int) arg2;
switch (cmd) {
case FSCONFIG_SET_BINARY:
case FSCONFIG_SET_STRING:
case FSCONFIG_SET_PATH:
case FSCONFIG_SET_PATH_EMPTY:
p3 = lock_user_string(arg3);
if (!p3) {
return -TARGET_EFAULT;
}
if (cmd != FSCONFIG_SET_BINARY) {
/* key and value must be strings. */
p4 = lock_user_string(arg4);
} else {
/*
* Otherwise the value must be a raw buffer with its
* length specified in arg5 (aux).
*/
p4 = lock_user(VERIFY_READ, arg4, arg5, 1);
}
if (!p4) {
unlock_user(p3, arg3, 0);
return -TARGET_EFAULT;
}
ret = get_errno(sys_fsconfig(arg1, arg2, p3, p4, arg5));
unlock_user(p3, arg3, 0);
unlock_user(p4, arg4, 0);
break;
case FSCONFIG_SET_FLAG:
case FSCONFIG_SET_FD:
/* arg4 (value) must be NULL. */
if (arg4) {
return -TARGET_EFAULT;
}
p3 = lock_user_string(arg3);
if (!p3) {
return -TARGET_EFAULT;
}
ret = get_errno(sys_fsconfig(arg1, arg2, p3, NULL, arg5));
unlock_user(p3, arg3, 0);
break;
case FSCONFIG_CMD_CREATE:
case FSCONFIG_CMD_RECONFIGURE:
#ifdef FSCONFIG_CMD_CREATE_EXCL
/*
* FSCONFIG_CMD_CREATE_EXCL is only available since Linux
* 6.6. Guarding it to allow building with pre-6.6 headers.
*/
case FSCONFIG_CMD_CREATE_EXCL:
#endif
/* key and value must be NULL, aux must be 0. */
if (arg3 || arg4 || arg5) {
return -TARGET_EFAULT;
}
ret = get_errno(sys_fsconfig(arg1, arg2, NULL, NULL, 0));
break;
default:
return -TARGET_EFAULT;
}
}
return ret;
case TARGET_NR_fsmount:
ret = get_errno(sys_fsmount(arg1, arg2, arg3));
return ret;
case TARGET_NR_fspick:
{
p = lock_user_string(arg2);
ret = get_errno(sys_fspick(arg1, p, arg3));
unlock_user(p, arg2, 0);
}
return ret;
#endif
default:
qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
return -TARGET_ENOSYS;