Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=f84e3f521e1449300e0fdc314b7b43b418a66dc3
Commit: f84e3f521e1449300e0fdc314b7b43b418a66dc3
Parent: e542059884bb6d651d7ffc64eacedbab2b64078c
Author: Miklos Szeredi <[EMAIL PROTECTED]>
AuthorDate: Fri Feb 8 04:21:34 2008 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Feb 8 09:22:39 2008 -0800
mount options: add documentation
This series addresses the problem of showing mount options in
/proc/mounts.
Several filesystems which use mount options, have not implemented a
.show_options superblock operation. Several others have implemented
this callback, but have not kept it fully up to date with the parsed
options.
Q: Why do we need correct option showing in /proc/mounts?
A: We want /proc/mounts to fully replace /etc/mtab. The reasons for
this are:
- unprivileged mounters won't be able to update /etc/mtab
- /etc/mtab doesn't work with private mount namespaces
- /etc/mtab can become out-of-sync with reality
Q: Can't this be done, so that filesystems need not bother with
implementing a .show_mounts callback, and keeping it up to date?
A: Only in some cases. Certain filesystems allow modification of a
subset of options in their remount_fs method. It is not possible
to take this into account without knowing exactly how the
filesystem handles options.
For the simple case (no remount or remount resets all options) the
patchset introduces two helpers:
generic_show_options()
save_mount_options()
These can also be used to emulate the old /etc/mtab behavior, until
proper support is added. Even if this is not 100% correct, it's still
better than showing no options at all.
The following patches fix up most in-tree filesystems, some have been
compile tested only, some have been reviewed and acked by the
maintainer.
Table displaying status of all in-kernel filesystems:
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
legend:
none - fs has options, but doesn't define ->show_options()
some - fs defines ->show_options(), but some only options are shown
good - fs shows all options
noopt - fs does not have options
patch - a patch will be posted
merged - a patch has been merged by subsystem maintainer
9p good
adfs patch
affs patch
afs patch
autofs patch
autofs4 patch
befs patch
bfs noopt
cifs some
coda noopt
configfs noopt
cramfs noopt
debugfs noopt
devpts patch
ecryptfs good
efs noopt
ext2 patch
ext3 good
ext4 merged
fat patch
freevxfs noopt
fuse patch
fusectl noopt
gfs2 good
gfs2meta noopt
hfs good
hfsplus good
hostfs patch
hpfs patch
hppfs noopt
hugetlbfs patch
isofs patch
jffs2 noopt
jfs merged
minix noopt
msdos ->fat
ncpfs patch
nfs some
nfsd noopt
ntfs good
ocfs2 good
ocfs2/dlmfs noopt
openpromfs noopt
proc noopt
qnx4 noopt
ramfs noopt
reiserfs patch
romfs noopt
smbfs good
sysfs noopt
sysv noopt
udf patch
ufs good
vfat ->fat
xfs good
mm/shmem.c patch
drivers/oprofile/oprofilefs.c noopt
drivers/infiniband/hw/ipath/ipath_fs.c noopt
drivers/misc/ibmasm/ibmasmfs.c noopt
drivers/usb/core (usbfs) merged
drivers/usb/gadget (gadgetfs) noopt
drivers/isdn/capi/capifs.c patch
kernel/cpuset.c noopt
fs/binfmt_misc.c noopt
net/sunrpc/rpc_pipe.c noopt
arch/powerpc/platforms/cell/spufs patch
arch/s390/hypfs good
ipc/mqueue.c noopt
security (securityfs) noopt
security/selinux/selinuxfs.c noopt
kernel/cgroup.c good
security/smack/smackfs.c noopt
in -mm:
reiser4 some
unionfs good
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This patch:
Document the rules for handling mount options in the .show_options
super operation.
Signed-off-by: Miklos Szeredi <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
Documentation/filesystems/vfs.txt | 50 ++++++++++++++++++++++++++++++++++--
1 files changed, 47 insertions(+), 3 deletions(-)
diff --git a/Documentation/filesystems/vfs.txt
b/Documentation/filesystems/vfs.txt
index bd55038..81e5be6 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -151,7 +151,7 @@ The get_sb() method has the following arguments:
const char *dev_name: the device name we are mounting.
void *data: arbitrary mount options, usually comes as an ASCII
- string
+ string (see "Mount Options" section)
struct vfsmount *mnt: a vfs-internal representation of a mount point
@@ -182,7 +182,7 @@ A fill_super() method implementation has the following
arguments:
must initialize this properly.
void *data: arbitrary mount options, usually comes as an ASCII
- string
+ string (see "Mount Options" section)
int silent: whether or not to be silent on error
@@ -291,7 +291,8 @@ or bottom half).
umount_begin: called when the VFS is unmounting a filesystem.
- show_options: called by the VFS to show mount options for /proc/<pid>/mounts.
+ show_options: called by the VFS to show mount options for
+ /proc/<pid>/mounts. (see "Mount Options" section)
quota_read: called by the VFS to read from filesystem quota file.
@@ -969,6 +970,49 @@ manipulate dentries:
For further information on dentry locking, please refer to the document
Documentation/filesystems/dentry-locking.txt.
+Mount Options
+=============
+
+Parsing options
+---------------
+
+On mount and remount the filesystem is passed a string containing a
+comma separated list of mount options. The options can have either of
+these forms:
+
+ option
+ option=value
+
+The <linux/parser.h> header defines an API that helps parse these
+options. There are plenty of examples on how to use it in existing
+filesystems.
+
+Showing options
+---------------
+
+If a filesystem accepts mount options, it must define show_options()
+to show all the currently active options. The rules are:
+
+ - options MUST be shown which are not default or their values differ
+ from the default
+
+ - options MAY be shown which are enabled by default or have their
+ default value
+
+Options used only internally between a mount helper and the kernel
+(such as file descriptors), or which only have an effect during the
+mounting (such as ones controlling the creation of a journal) are exempt
+from the above rules.
+
+The underlying reason for the above rules is to make sure, that a
+mount can be accurately replicated (e.g. umounting and mounting again)
+based on the information found in /proc/mounts.
+
+A simple method of saving options at mount/remount time and showing
+them is provided with the save_mount_options() and
+generic_show_options() helper functions. Please note, that using
+these may have drawbacks. For more info see header comments for these
+functions in fs/namespace.c.
Resources
=========
-
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
