Re: [PATCH v5 8/8] linux: Add mount_setattr

[Yann Droneaud <ydroneaud@opteya.com>]

Hi,

Le 06/06/2022 à 15:44, Adhemerval Zanella via Libc-alpha a écrit :
> It was added on Linux 5.12 (2a1867219c7b27f928e2545782b86daaf9ad50bd)
> to allow change the properties of a mount or a mount tree using file
> descriptors which the new mount api is based on.
>
> Checked on x86_64-linux-gnu.
> ---
>   NEWS                                          |  6 ++--
>   sysdeps/unix/sysv/linux/Versions              |  1 +
>   sysdeps/unix/sysv/linux/aarch64/libc.abilist  |  1 +
>   sysdeps/unix/sysv/linux/alpha/libc.abilist    |  1 +
>   sysdeps/unix/sysv/linux/arc/libc.abilist      |  1 +
>   sysdeps/unix/sysv/linux/arm/be/libc.abilist   |  1 +
>   sysdeps/unix/sysv/linux/arm/le/libc.abilist   |  1 +
>   sysdeps/unix/sysv/linux/csky/libc.abilist     |  1 +
>   sysdeps/unix/sysv/linux/hppa/libc.abilist     |  1 +
>   sysdeps/unix/sysv/linux/i386/libc.abilist     |  1 +
>   sysdeps/unix/sysv/linux/ia64/libc.abilist     |  1 +
>   .../sysv/linux/m68k/coldfire/libc.abilist     |  1 +
>   .../unix/sysv/linux/m68k/m680x0/libc.abilist  |  1 +
>   .../sysv/linux/microblaze/be/libc.abilist     |  1 +
>   .../sysv/linux/microblaze/le/libc.abilist     |  1 +
>   .../sysv/linux/mips/mips32/fpu/libc.abilist   |  1 +
>   .../sysv/linux/mips/mips32/nofpu/libc.abilist |  1 +
>   .../sysv/linux/mips/mips64/n32/libc.abilist   |  1 +
>   .../sysv/linux/mips/mips64/n64/libc.abilist   |  1 +
>   sysdeps/unix/sysv/linux/nios2/libc.abilist    |  1 +
>   sysdeps/unix/sysv/linux/or1k/libc.abilist     |  1 +
>   .../linux/powerpc/powerpc32/fpu/libc.abilist  |  1 +
>   .../powerpc/powerpc32/nofpu/libc.abilist      |  1 +
>   .../linux/powerpc/powerpc64/be/libc.abilist   |  1 +
>   .../linux/powerpc/powerpc64/le/libc.abilist   |  1 +
>   .../unix/sysv/linux/riscv/rv32/libc.abilist   |  1 +
>   .../unix/sysv/linux/riscv/rv64/libc.abilist   |  1 +
>   .../unix/sysv/linux/s390/s390-32/libc.abilist |  1 +
>   .../unix/sysv/linux/s390/s390-64/libc.abilist |  1 +
>   sysdeps/unix/sysv/linux/sh/be/libc.abilist    |  1 +
>   sysdeps/unix/sysv/linux/sh/le/libc.abilist    |  1 +
>   .../sysv/linux/sparc/sparc32/libc.abilist     |  1 +
>   .../sysv/linux/sparc/sparc64/libc.abilist     |  1 +
>   sysdeps/unix/sysv/linux/sys/mount.h           | 22 ++++++++++++++
>   sysdeps/unix/sysv/linux/syscalls.list         |  1 +
>   sysdeps/unix/sysv/linux/tst-mount.c           | 30 +++++++++++++++++--
>   .../unix/sysv/linux/x86_64/64/libc.abilist    |  1 +
>   .../unix/sysv/linux/x86_64/x32/libc.abilist   |  1 +
>   38 files changed, 87 insertions(+), 6 deletions(-)
>
> diff --git a/NEWS b/NEWS
> index de12657449..696de3962b 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -29,9 +29,9 @@ Major new features:
>     memory is carried out in the context of the caller, using the caller's
>     CPU affinity, and priority with CPU usage accounted to the caller.
>   
> -* On Linux, the fsopen, fsmount, move_mount, fsconfig, fspick, and open_tree
> -  have been added.  It is a new mount API to allow more flexibility on mount
> -  operations, specially when used along namespaces.
> +* On Linux, the fsopen, fsmount, move_mount, fsconfig, fspick, open_tree,
> +  and mount_setattr have been added.  It is a new mount API to allow more
> +  flexibility on mount operations, specially when used along namespaces.
>   
>   Deprecated and removed features, and other changes affecting compatibility:
>   
> diff --git a/sysdeps/unix/sysv/linux/Versions b/sysdeps/unix/sysv/linux/Versions
> index b70530ef40..65d2ceda2c 100644
> --- a/sysdeps/unix/sysv/linux/Versions
> +++ b/sysdeps/unix/sysv/linux/Versions
> @@ -305,6 +305,7 @@ libc {
>       fsopen;
>       fspick;
>       move_mount;
> +    mount_setattr;
>       open_tree;
>       pidfd_open;
>       pidfd_getfd;

> diff --git a/sysdeps/unix/sysv/linux/sys/mount.h b/sysdeps/unix/sysv/linux/sys/mount.h
> index eb6705a091..4929d84027 100644
> --- a/sysdeps/unix/sysv/linux/sys/mount.h
> +++ b/sysdeps/unix/sysv/linux/sys/mount.h
> @@ -23,6 +23,8 @@
>   
>   #include <fcntl.h>
>   #include <features.h>
> +#include <stdint.h>
> +#include <stddef.h>
>   #include <sys/ioctl.h>
>   
>   #define BLOCK_SIZE	1024
> @@ -155,6 +157,17 @@ enum
>   #define MOUNT_ATTR_NOSYMFOLLOW  0x00200000 /* Do not follow symlinks.  */
>   
>   
> +/* For mount_setattr.  */
> +struct mount_attr
> +{
> +  uint64_t attr_set;
> +  uint64_t attr_clr;
> +  uint64_t propagation;
> +  uint64_t userns_fd;
> +};
> +
> +#define MOUNT_ATTR_SIZE_VER0    32 /* sizeof first published struct */
> +
>   /* move_mount flags.  */
>   #define MOVE_MOUNT_F_SYMLINKS   0x00000001 /* Follow symlinks on from path */
>   #define MOVE_MOUNT_F_AUTOMOUNTS 0x00000002 /* Follow automounts on from path */
> @@ -240,6 +253,15 @@ extern int fspick (int __dfd, const char *__path, unsigned int __flags)
>   extern int open_tree (int __dfd, const char *__filename, unsigned int __flags)
>     __THROW;
>   
> +/* Change the mount proprieties of the mount or an entire mount tree.  If
> +   PATH is a relative pathname, then it is interpreted relative to the directory
> +   referred to by the file descriptor dirfd.  Otherwise if DFD is the special
> +   value AT_FDCWD then PATH is interpreted relative to the current working
> +   directory of the calling process.  */
> +extern int mount_setattr (int __dfd, const char *__path, unsigned int __flags,
> +			  struct mount_attr *__uattr, size_t __usize)
> +  __THROW;
> +


I wonder why __uattr is not declared const struct mount_attr * ?

Is it really expected that future mount_setattr() extensions to write 
back into the userspace structure ?



>   __END_DECLS
>   
>   #endif /* _SYS_MOUNT_H */
> diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
> index e5e2b528fd..f79a519d89 100644
> --- a/sysdeps/unix/sysv/linux/syscalls.list
> +++ b/sysdeps/unix/sysv/linux/syscalls.list
> @@ -39,6 +39,7 @@ mincore		-	mincore		i:aUV	mincore
>   mlock		-	mlock		i:bU	mlock
>   mlockall	-	mlockall	i:i	mlockall
>   mount		EXTRA	mount		i:sssUp	__mount	mount
> +mount_setattr	EXTRA	mount_setattr	i:isUpi	mount_setattr
>   move_mount	EXTRA	move_mount	i:isisU	move_mount
>   munlock		-	munlock		i:aU	munlock
>   munlockall	-	munlockall	i:	munlockall


Regards

-- 

Yann Droneaud

OPTEYA