diff mbox series

[v6,1/2] statmount.2: New page describing the statmount syscall

Message ID 5b4a8408a21970d0ee4bea5cee4c74cb39851c0d.1720549824.git.josef@toxicpanda.com (mailing list archive)
State New
Headers show
Series man-pages: add documentation for statmount/listmount | expand

Commit Message

Josef Bacik July 9, 2024, 6:31 p.m. UTC 
Add some documentation on the new statmount syscall.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 man/man2/statmount.2 | 281 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 281 insertions(+)
 create mode 100644 man/man2/statmount.2

Comments

Alejandro Colomar July 9, 2024, 7:32 p.m. UTC | #1 
Hi Josef,

On Tue, Jul 09, 2024 at 02:31:22PM GMT, Josef Bacik wrote:
> Add some documentation on the new statmount syscall.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

I've applied the patch, with some tweaks.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=1e607c20633d839d9241da50071d508ef617f878>

Have a lovely day!
Alex


diff --git i/man/man2/statmount.2 w/man/man2/statmount.2
index 2ae1f1bc3..4b54a6c85 100644
--- i/man/man2/statmount.2
+++ w/man/man2/statmount.2
@@ -14,40 +14,42 @@ .SH SYNOPSIS
 .BR "#include <linux/mount.h>" "  /* Definition of STATMOUNT_* constants */"
 .B #include <unistd.h>
 .P
-.BI "int syscall(SYS_statmount, struct mnt_id_req * " req ,
-.BI "            struct statmount * " smbuf ", size_t " bufsize ,
+.BI "int syscall(SYS_statmount, struct mnt_id_req *" req ,
+.BI "            struct statmount *" smbuf ", size_t " bufsize ,
 .BI "            unsigned long " flags );
 .P
 .B #include <linux/mount.h>
+.fi
 .P
+.EX
 .B struct mnt_id_req {
-.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
-.BR "    __u64 mnt_id;" "  /* The mnt_id being queried */"
-.BR "    __u64 param;" "   /* An ORed combination of the STATMOUNT_ constants */"
+.BR "    __u32  size;" "    /* sizeof(struct mnt_id_req) */"
+.BR "    __u64  mnt_id;" "  /* The mnt_id being queried */"
+.BR "    __u64  param;" "   /* An ORed combination of the STATMOUNT_ constants */"
 .B };
 .P
 .B struct statmount {
-.B "    __u32 size;"
-.B "    __u64 mask;"
-.B "    __u32 sb_dev_major;"
-.B "    __u32 sb_dev_minor;"
-.B "    __u64 sb_magic;"
-.B "    __u32 sb_flags;"
-.B "    __u32 fs_type;"
-.B "    __u64 mnt_id;"
-.B "    __u64 mnt_parent_id;"
-.B "    __u32 mnt_id_old;"
-.B "    __u32 mnt_parent_id_old;"
-.B "    __u64 mnt_attr;"
-.B "    __u64 mnt_propagation;"
-.B "    __u64 mnt_peer_group;"
-.B "    __u64 mnt_master;"
-.B "    __u64 propagate_from;"
-.B "    __u32 mnt_root;"
-.B "    __u32 mnt_point;"
-.B "    char  str[];"
+.B "    __u32  size;"
+.B "    __u64  mask;"
+.B "    __u32  sb_dev_major;"
+.B "    __u32  sb_dev_minor;"
+.B "    __u64  sb_magic;"
+.B "    __u32  sb_flags;"
+.B "    __u32  fs_type;"
+.B "    __u64  mnt_id;"
+.B "    __u64  mnt_parent_id;"
+.B "    __u32  mnt_id_old;"
+.B "    __u32  mnt_parent_id_old;"
+.B "    __u64  mnt_attr;"
+.B "    __u64  mnt_propagation;"
+.B "    __u64  mnt_peer_group;"
+.B "    __u64  mnt_master;"
+.B "    __u64  propagate_from;"
+.B "    __u32  mnt_root;"
+.B "    __u32  mnt_point;"
+.B "    char   str[];"
 .B };
-.fi
+.EE
 .P
 .IR Note :
 glibc provides no wrapper for
@@ -117,7 +119,7 @@ .SS The mnt_id_req structure
 .I statmount.mask
 field.
 Therefore,
-.I "do not"
+.I do not
 simply set
 .I req.param
 to



> ---
>  man/man2/statmount.2 | 281 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 281 insertions(+)
>  create mode 100644 man/man2/statmount.2
> 
> diff --git a/man/man2/statmount.2 b/man/man2/statmount.2
> new file mode 100644
> index 000000000..2ae1f1bc3
> --- /dev/null
> +++ b/man/man2/statmount.2
> @@ -0,0 +1,281 @@
> +'\" t
> +.\" Copyright (c) 2024 Josef Bacik <josef@toxicpanda.com>
> +.\"
> +.\" SPDX-License-Identifier: Linux-man-pages-copyleft
> +.\"
> +.TH statmount 2 (date) "Linux man-pages (unreleased)"
> +.SH NAME
> +statmount \- get a mount status
> +.SH LIBRARY
> +Standard C library
> +.RI ( libc ", " \-lc )
> +.SH SYNOPSIS
> +.nf
> +.BR "#include <linux/mount.h>" "  /* Definition of STATMOUNT_* constants */"
> +.B #include <unistd.h>
> +.P
> +.BI "int syscall(SYS_statmount, struct mnt_id_req * " req ,
> +.BI "            struct statmount * " smbuf ", size_t " bufsize ,
> +.BI "            unsigned long " flags );
> +.P
> +.B #include <linux/mount.h>
> +.P
> +.B struct mnt_id_req {
> +.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
> +.BR "    __u64 mnt_id;" "  /* The mnt_id being queried */"
> +.BR "    __u64 param;" "   /* An ORed combination of the STATMOUNT_ constants */"
> +.B };
> +.P
> +.B struct statmount {
> +.B "    __u32 size;"
> +.B "    __u64 mask;"
> +.B "    __u32 sb_dev_major;"
> +.B "    __u32 sb_dev_minor;"
> +.B "    __u64 sb_magic;"
> +.B "    __u32 sb_flags;"
> +.B "    __u32 fs_type;"
> +.B "    __u64 mnt_id;"
> +.B "    __u64 mnt_parent_id;"
> +.B "    __u32 mnt_id_old;"
> +.B "    __u32 mnt_parent_id_old;"
> +.B "    __u64 mnt_attr;"
> +.B "    __u64 mnt_propagation;"
> +.B "    __u64 mnt_peer_group;"
> +.B "    __u64 mnt_master;"
> +.B "    __u64 propagate_from;"
> +.B "    __u32 mnt_root;"
> +.B "    __u32 mnt_point;"
> +.B "    char  str[];"
> +.B };
> +.fi
> +.P
> +.IR Note :
> +glibc provides no wrapper for
> +.BR statmount (),
> +necessitating the use of
> +.BR syscall (2).
> +.SH DESCRIPTION
> +To access a mount's status,
> +the caller must have CAP_SYS_ADMIN in the user namespace.
> +.P
> +This function returns information about a mount,
> +storing it in the buffer pointed to by
> +.IR smbuf .
> +The returned buffer is a
> +.I struct statmount
> +which is of size
> +.I bufsize
> +with the fields filled in as described below.
> +.P
> +(Note that reserved space and padding is omitted.)
> +.SS The mnt_id_req structure
> +.I req.size
> +is used by the kernel to determine which
> +.I struct\~mnt_id_req
> +is being passed in;
> +it should always be set to
> +.IR sizeof(struct\~mnt_id_req) .
> +.P
> +.I req.mnt_id
> +can be obtained from either
> +.BR statx (2)
> +using
> +.B STATX_MNT_ID_UNIQUE
> +or from
> +.BR listmount (2)
> +and is used as the identifier to query the status of the desired mount point.
> +.P
> +.I req.param
> +is used to tell the kernel which fields the caller is interested in.
> +It is an ORed combination of the following constants
> +.P
> +.in +4n
> +.TS
> +lB l.
> +STATMOUNT_SB_BASIC	/* Want/got sb_* */
> +STATMOUNT_MNT_BASIC	/* Want/got mnt_* */
> +STATMOUNT_PROPAGATE_FROM	/* Want/got propagate_from */
> +STATMOUNT_MNT_ROOT	/* Want/got mnt_root  */
> +STATMOUNT_MNT_POINT	/* Want/got mnt_point */
> +STATMOUNT_FS_TYPE	/* Want/got fs_type */
> +.TE
> +.in
> +.P
> +In general,
> +the kernel does
> +.I not
> +reject values in
> +.I req.param
> +other than the above.
> +(For an exception,
> +see
> +.B EINVAL
> +in errors.)
> +Instead,
> +it simply informs the caller which values are supported
> +by this kernel and filesystem via the
> +.I statmount.mask
> +field.
> +Therefore,
> +.I "do not"
> +simply set
> +.I req.param
> +to
> +.B UINT_MAX
> +(all bits set),
> +as one or more bits may,
> +in the future,
> +be used to specify an extension to the buffer.
> +.SS The returned information
> +The status information for the target mount is returned in the
> +.I statmount
> +structure pointed to by
> +.IR smbuf .
> +.P
> +The fields in the
> +.I statmount
> +structure are:
> +.TP
> +.I smbuf.size
> +The size of the returned
> +.I smbuf
> +structure,
> +including any of the strings fields that were filled.
> +.TP
> +.I smbuf.mask
> +The ORed combination of
> +.BI STATMOUNT_ *
> +flags indicating which fields were filled in and thus valid.
> +The kernel may return fields that weren't requested,
> +and may fail to return fields that were requested,
> +depending on what the backing file system and kernel supports.
> +In either case,
> +.I req.param
> +will not be equal to
> +.IR mask .
> +.TP
> +.I smbuf.sb_dev_major
> +.TQ
> +.I smbuf.sb_dev_minor
> +The device that is mounted at this mount point.
> +.TP
> +.I smbuf.sb_magic
> +The file system specific super block magic.
> +.TP
> +.I smbuf.sb_flags
> +The flags that are set on the super block,
> +an ORed combination of
> +.BR SB_RDONLY ,
> +.BR SB_SYNCHRONOUS ,
> +.BR SB_DIRSYNC ,
> +.BR SB_LAZYTIME .
> +.TP
> +.I smbuf.fs_type
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mounted file system.
> +It is a null-terminated string.
> +.TP
> +.I smbuf.mnt_id
> +The unique mount ID of the mount.
> +.TP
> +.I smbuf.mnt_parent_id
> +The unique mount ID of the parent mount point of this mount.
> +If this is the root mount point then
> +.IR smbuf.mnt_id\~==\~smbuf.parent_mount_id .
> +.TP
> +.I smbuf.mnt_id_old
> +This corresponds to the mount ID that is exported by
> +.IR /proc/ pid /mountinfo .
> +.TP
> +.I smbuf.mnt_parent_id_old
> +This corresponds to the parent mount ID that is exported by
> +.IR /proc/ pid /mountinfo .
> +.TP
> +.I smbuf.mnt_attr
> +The
> +.BI MOUNT_ATTR_ *
> +flags set on this mount point.
> +.TP
> +.I smbuf.mnt_propagation
> +The mount propagation flags,
> +which can be one of
> +.BR MS_SHARED ,
> +.BR MS_SLAVE ,
> +.BR MS_PRIVATE ,
> +.BR MS_UNBINDABLE .
> +.TP
> +.I smbuf.mnt_peer_group
> +The ID of the shared peer group.
> +.TP
> +.I smbuf.mnt_master
> +The mount point receives its propagation from this mount ID.
> +.TP
> +.I smbuf.propagate_from
> +The ID from the namespace we propagated from.
> +.TP
> +.I smbuf.mnt_root
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mount
> +relative to the root of the file system.
> +It is a null-terminated string.
> +.TP
> +.I smbuf.mnt_point
> +The offset to the location in the
> +.I smbuf.str
> +buffer that contains the string representation of the mount
> +relative to the current root (ie if you are in a
> +.BR chroot ).
> +It is a null-terminated string.
> +.SH RETURN VALUE
> +On success, zero is returned.
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EPERM
> +Permission is denied for accessing this mount.
> +.TP
> +.B EFAULT
> +.I req
> +or
> +.I smbuf
> +points to a location outside the process's accessible
> +address space.
> +.TP
> +.B EINVAL
> +Invalid flag specified in
> +.IR flags .
> +.TP
> +.B EINVAL
> +.I req
> +is of insufficient size to be utilized.
> +.TP
> +.B E2BIG
> +.I req
> +is too large.
> +.TP
> +.B EOVERFLOW
> +The size of
> +.I smbuf
> +is too small to contain either the
> +.IR smbuf.fs_type ,
> +.IR smbuf.mnt_root ,
> +or
> +.IR smbuf.mnt_point .
> +Allocate a larger buffer and retry the call.
> +.TP
> +.B ENOENT
> +The specified
> +.I req.mnt_id
> +doesn't exist.
> +.TP
> +.B ENOMEM
> +Out of memory (i.e., kernel memory).
> +.SH STANDARDS
> +Linux.
> +.SH SEE ALSO
> +.BR listmount (2),
> +.BR statx (2)
> -- 
> 2.43.0
> 
>
diff mbox series

Patch

diff --git a/man/man2/statmount.2 b/man/man2/statmount.2
new file mode 100644
index 000000000..2ae1f1bc3
--- /dev/null
+++ b/man/man2/statmount.2
@@ -0,0 +1,281 @@ 
+'\" t
+.\" Copyright (c) 2024 Josef Bacik <josef@toxicpanda.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH statmount 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+statmount \- get a mount status
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/mount.h>" "  /* Definition of STATMOUNT_* constants */"
+.B #include <unistd.h>
+.P
+.BI "int syscall(SYS_statmount, struct mnt_id_req * " req ,
+.BI "            struct statmount * " smbuf ", size_t " bufsize ,
+.BI "            unsigned long " flags );
+.P
+.B #include <linux/mount.h>
+.P
+.B struct mnt_id_req {
+.BR "    __u32 size;" "    /* sizeof(struct mnt_id_req) */"
+.BR "    __u64 mnt_id;" "  /* The mnt_id being queried */"
+.BR "    __u64 param;" "   /* An ORed combination of the STATMOUNT_ constants */"
+.B };
+.P
+.B struct statmount {
+.B "    __u32 size;"
+.B "    __u64 mask;"
+.B "    __u32 sb_dev_major;"
+.B "    __u32 sb_dev_minor;"
+.B "    __u64 sb_magic;"
+.B "    __u32 sb_flags;"
+.B "    __u32 fs_type;"
+.B "    __u64 mnt_id;"
+.B "    __u64 mnt_parent_id;"
+.B "    __u32 mnt_id_old;"
+.B "    __u32 mnt_parent_id_old;"
+.B "    __u64 mnt_attr;"
+.B "    __u64 mnt_propagation;"
+.B "    __u64 mnt_peer_group;"
+.B "    __u64 mnt_master;"
+.B "    __u64 propagate_from;"
+.B "    __u32 mnt_root;"
+.B "    __u32 mnt_point;"
+.B "    char  str[];"
+.B };
+.fi
+.P
+.IR Note :
+glibc provides no wrapper for
+.BR statmount (),
+necessitating the use of
+.BR syscall (2).
+.SH DESCRIPTION
+To access a mount's status,
+the caller must have CAP_SYS_ADMIN in the user namespace.
+.P
+This function returns information about a mount,
+storing it in the buffer pointed to by
+.IR smbuf .
+The returned buffer is a
+.I struct statmount
+which is of size
+.I bufsize
+with the fields filled in as described below.
+.P
+(Note that reserved space and padding is omitted.)
+.SS The mnt_id_req structure
+.I req.size
+is used by the kernel to determine which
+.I struct\~mnt_id_req
+is being passed in;
+it should always be set to
+.IR sizeof(struct\~mnt_id_req) .
+.P
+.I req.mnt_id
+can be obtained from either
+.BR statx (2)
+using
+.B STATX_MNT_ID_UNIQUE
+or from
+.BR listmount (2)
+and is used as the identifier to query the status of the desired mount point.
+.P
+.I req.param
+is used to tell the kernel which fields the caller is interested in.
+It is an ORed combination of the following constants
+.P
+.in +4n
+.TS
+lB l.
+STATMOUNT_SB_BASIC	/* Want/got sb_* */
+STATMOUNT_MNT_BASIC	/* Want/got mnt_* */
+STATMOUNT_PROPAGATE_FROM	/* Want/got propagate_from */
+STATMOUNT_MNT_ROOT	/* Want/got mnt_root  */
+STATMOUNT_MNT_POINT	/* Want/got mnt_point */
+STATMOUNT_FS_TYPE	/* Want/got fs_type */
+.TE
+.in
+.P
+In general,
+the kernel does
+.I not
+reject values in
+.I req.param
+other than the above.
+(For an exception,
+see
+.B EINVAL
+in errors.)
+Instead,
+it simply informs the caller which values are supported
+by this kernel and filesystem via the
+.I statmount.mask
+field.
+Therefore,
+.I "do not"
+simply set
+.I req.param
+to
+.B UINT_MAX
+(all bits set),
+as one or more bits may,
+in the future,
+be used to specify an extension to the buffer.
+.SS The returned information
+The status information for the target mount is returned in the
+.I statmount
+structure pointed to by
+.IR smbuf .
+.P
+The fields in the
+.I statmount
+structure are:
+.TP
+.I smbuf.size
+The size of the returned
+.I smbuf
+structure,
+including any of the strings fields that were filled.
+.TP
+.I smbuf.mask
+The ORed combination of
+.BI STATMOUNT_ *
+flags indicating which fields were filled in and thus valid.
+The kernel may return fields that weren't requested,
+and may fail to return fields that were requested,
+depending on what the backing file system and kernel supports.
+In either case,
+.I req.param
+will not be equal to
+.IR mask .
+.TP
+.I smbuf.sb_dev_major
+.TQ
+.I smbuf.sb_dev_minor
+The device that is mounted at this mount point.
+.TP
+.I smbuf.sb_magic
+The file system specific super block magic.
+.TP
+.I smbuf.sb_flags
+The flags that are set on the super block,
+an ORed combination of
+.BR SB_RDONLY ,
+.BR SB_SYNCHRONOUS ,
+.BR SB_DIRSYNC ,
+.BR SB_LAZYTIME .
+.TP
+.I smbuf.fs_type
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mounted file system.
+It is a null-terminated string.
+.TP
+.I smbuf.mnt_id
+The unique mount ID of the mount.
+.TP
+.I smbuf.mnt_parent_id
+The unique mount ID of the parent mount point of this mount.
+If this is the root mount point then
+.IR smbuf.mnt_id\~==\~smbuf.parent_mount_id .
+.TP
+.I smbuf.mnt_id_old
+This corresponds to the mount ID that is exported by
+.IR /proc/ pid /mountinfo .
+.TP
+.I smbuf.mnt_parent_id_old
+This corresponds to the parent mount ID that is exported by
+.IR /proc/ pid /mountinfo .
+.TP
+.I smbuf.mnt_attr
+The
+.BI MOUNT_ATTR_ *
+flags set on this mount point.
+.TP
+.I smbuf.mnt_propagation
+The mount propagation flags,
+which can be one of
+.BR MS_SHARED ,
+.BR MS_SLAVE ,
+.BR MS_PRIVATE ,
+.BR MS_UNBINDABLE .
+.TP
+.I smbuf.mnt_peer_group
+The ID of the shared peer group.
+.TP
+.I smbuf.mnt_master
+The mount point receives its propagation from this mount ID.
+.TP
+.I smbuf.propagate_from
+The ID from the namespace we propagated from.
+.TP
+.I smbuf.mnt_root
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mount
+relative to the root of the file system.
+It is a null-terminated string.
+.TP
+.I smbuf.mnt_point
+The offset to the location in the
+.I smbuf.str
+buffer that contains the string representation of the mount
+relative to the current root (ie if you are in a
+.BR chroot ).
+It is a null-terminated string.
+.SH RETURN VALUE
+On success, zero is returned.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EPERM
+Permission is denied for accessing this mount.
+.TP
+.B EFAULT
+.I req
+or
+.I smbuf
+points to a location outside the process's accessible
+address space.
+.TP
+.B EINVAL
+Invalid flag specified in
+.IR flags .
+.TP
+.B EINVAL
+.I req
+is of insufficient size to be utilized.
+.TP
+.B E2BIG
+.I req
+is too large.
+.TP
+.B EOVERFLOW
+The size of
+.I smbuf
+is too small to contain either the
+.IR smbuf.fs_type ,
+.IR smbuf.mnt_root ,
+or
+.IR smbuf.mnt_point .
+Allocate a larger buffer and retry the call.
+.TP
+.B ENOENT
+The specified
+.I req.mnt_id
+doesn't exist.
+.TP
+.B ENOMEM
+Out of memory (i.e., kernel memory).
+.SH STANDARDS
+Linux.
+.SH SEE ALSO
+.BR listmount (2),
+.BR statx (2)