| Message ID | 85889ca0f88e79e79bc8bfeb58395c04affe3424.1719840964.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | man-pages: add documentation for statmount/listmount | expand |
Hi Josef, On Mon, Jul 01, 2024 at 09:37:53AM GMT, Josef Bacik wrote: > Add some documentation on the new statmount syscall. > > Signed-off-by: Josef Bacik <josef@toxicpanda.com> > --- > man/man2/statmount.2 | 288 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 288 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..3e13107f5 > --- /dev/null > +++ b/man/man2/statmount.2 > @@ -0,0 +1,288 @@ > +'\" 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 , Nothing in the page describes bufsize, AFAICS. $ grep bufsize man/man2/statmount.2 | wc -l 1 > +.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, > +you must have CAP_SYS_ADMIN in the user namespace. s/you/the caller/ > +.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 > +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 struct > +.I mnt_id_req If you use 'struct\~foo', both words should be in italics. You can do that, or make only 'foo' italics, and say foo structure. > +is being passed in, s/,/;/ > +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 > +lBl. Let's put some space there: 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 > +Note that, I'd remove the above, and start with "In general, ...". Usually, everything is noteworthy, and if not, it should not go into the documentation, or go into a footnote where it's marked as "unnecessary on a first reading". :) See also: <https://lore.kernel.org/linux-man/20230105225235.6cjtz6orjzxzvo6v@illithid/> > +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 . I think I'd move the text after this point to the descriptions of smbuf.size and smbuf.mask. > +Included in this is > +.I size > +which indicates the size of the > +.I smbuf > +that was filled in, > +including any strings. > +.I mask > +which indicates what information in the structure has been filled in. > +.P > +It should be noted that the kernel may return fields that weren't requested s/It should be noted that the/The/ For the reasons noted above. > +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 . > +.P > +The fields in the > +.I statmount > +structure are: > +.TP > +.I smbuf.size > +The size of the returned > +.I smbuf > +structure. > +.TP > +.I smbuf.mask > +The ORed combination of > +.B STATMOUNT_ .BI STATMOUNT_ * > +flags indicating which fields were filled in and thus valid. > +.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 New sentence, new line. > +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 I'd break the line right before "relative". > +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 I'd break the line right before "relative". > +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 > +is NULL or 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. > +.B E2BIG > +.I req > +is too large, > +the limit is the architectures page size. I think the user should not know that the limit is a page size. The user shall specify it as sizeof(struct mnt_id_req), and should ignore any implementation details of the kernel. So: "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 Have a lovely day! Alex
diff --git a/man/man2/statmount.2 b/man/man2/statmount.2 new file mode 100644 index 000000000..3e13107f5 --- /dev/null +++ b/man/man2/statmount.2 @@ -0,0 +1,288 @@ +'\" 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, +you 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 +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 struct +.I 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 +lBl. +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 +Note that, +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 . +Included in this is +.I size +which indicates the size of the +.I smbuf +that was filled in, +including any strings. +.I mask +which indicates what information in the structure has been filled in. +.P +It should be noted that 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 . +.P +The fields in the +.I statmount +structure are: +.TP +.I smbuf.size +The size of the returned +.I smbuf +structure. +.TP +.I smbuf.mask +The ORed combination of +.B STATMOUNT_ +flags indicating which fields were filled in and thus valid. +.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 +is NULL or 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. +.B E2BIG +.I req +is too large, +the limit is the architectures page size. +.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)
Add some documentation on the new statmount syscall. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- man/man2/statmount.2 | 288 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 288 insertions(+) create mode 100644 man/man2/statmount.2