Hello all.
As found by some of my students, mount(2) lacks description of some
flags used by userland. After trying to sync things out, I realized
that this page is not well organized at all. For example, unmount
syscall is mentioned closer to end, after description of flags that
it could use.
I didn't document all of the flags involved in mount calls, since
some of them are purely kernel internal. But I could easily miss
something crucial...
So this is my first public draft of mount(2) patch. Looking for
comments & thanks in advance!
--
WBR,
Vadim Zhukov
Index: mount.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/mount.2,v
retrieving revision 1.46
diff -u -p -r1.46 mount.2
--- mount.2 27 May 2016 19:45:04 -0000 1.46
+++ mount.2 9 Jul 2016 15:16:29 -0000
@@ -70,31 +70,57 @@ at the time
of a successful mount are swept under the carpet, so to speak, and
are unavailable until the filesystem is unmounted.
.Pp
+The
+.Fn unmount
+function call disassociates the filesystem from the specified
+mount point
+.Fa dir .
+.Pp
The following
.Fa flags
may be specified to
suppress default semantics which affect filesystem access.
.Bl -tag -width MNT_SYNCHRONOUS
-.It Dv MNT_RDONLY
-The filesystem should be treated as read-only:
-even the superuser may not write to it.
+.It Dv MNT_ASYNC
+All I/O to the filesystem should be done asynchronously.
+.It Dv MNT_FORCE
+On unmount, specifies that the filesystem should be forcibly unmounted
+even if files are still active.
+Active special devices continue to work,
+but any further accesses to any other active files result in errors
+even if the filesystem is later remounted.
+On update, allows to forcibly change from read-write to read-only,
+even if there are files open for writing.
.It Dv MNT_NOATIME
Do not update the access time on files in the filesystem unless
the modification or status change times are also being updated.
+.It Dv MNT_NODEV
+Do not interpret special files on the filesystem.
.It Dv MNT_NOEXEC
Do not allow files to be executed from the filesystem.
.It Dv MNT_NOSUID
Do not honor setuid or setgid bits on files when executing them.
-.It Dv MNT_NODEV
-Do not interpret special files on the filesystem.
-.It Dv MNT_SYNCHRONOUS
-All I/O to the filesystem should be done synchronously.
-.It Dv MNT_ASYNC
-All I/O to the filesystem should be done asynchronously.
+.It Dv MNT_RDONLY
+The filesystem should be treated as read-only:
+even the superuser may not write to it.
+.It Dv MNT_RELOAD
+Reload already mounted filesystem.
+Used, e.g., by
+.Xr fsck 8 .
.It Dv MNT_SOFTDEP
Use soft dependencies.
Applies to FFS filesystems only (see 'softdep' in
.Xr mount 8 ) .
+.It Dv MNT_SYNCHRONOUS
+All I/O to the filesystem should be done synchronously.
+.It Dv MNT_UPDATE
+Indicates that the mount command is being applied to an already mounted
+filesystem.
+This allows the mount flags to be changed without requiring
+that the filesystem be unmounted and remounted.
+Some filesystems may not allow all flags to be changed.
+For example,
+most filesystems will not allow a change from read-write to read-only.
.It MNT_WXALLOWED
Processes that ask for memory to be made writeable plus executable
using the
@@ -108,16 +134,6 @@ The option is typically used on the
filesystem.
.El
.Pp
-The flag
-.Dv MNT_UPDATE
-indicates that the mount command is being applied
-to an already mounted filesystem.
-This allows the mount flags to be changed without requiring
-that the filesystem be unmounted and remounted.
-Some filesystems may not allow all flags to be changed.
-For example,
-most filesystems will not allow a change from read-write to read-only.
-.Pp
The
.Fa type
argument defines the type of the filesystem.
@@ -237,22 +253,6 @@ struct udf_args {
char *fspec; /* block special device to mount */
};
.Ed
-.Pp
-The
-.Fn unmount
-function call disassociates the filesystem from the specified
-mount point
-.Fa dir .
-.Pp
-The
-.Fa flags
-argument may specify
-.Dv MNT_FORCE
-to specify that the filesystem should be forcibly unmounted even if files are
-still active.
-Active special devices continue to work,
-but any further accesses to any other active files result in errors
-even if the filesystem is later remounted.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
