Re: [PATCH 15/28] VFS: Mountpoint file descriptor umount support

[Mike Waychison <Michael.Waychison@Sun.COM>]

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Christoph Hellwig wrote:
> On Mon, Oct 25, 2004 at 10:46:09AM -0400, Mike Waychison wrote:
> 
>>This patch adds functionality to mountfd so that a user can perform the
>>various types of umount (forced umount, not-busy umount, lazy-umount).
>>
>>Signed-off-by: Mike Waychison <michael.waychison@sun.com>
>>---
>>
>> fs/mountfd.c       |   20 ++++++++++++++++++++
>> fs/namespace.c     |    2 +-
>> include/linux/fs.h |    5 ++++-
>> 3 files changed, 25 insertions(+), 2 deletions(-)
>>
>>Index: linux-2.6.9-quilt/fs/mountfd.c
>>===================================================================
>>--- linux-2.6.9-quilt.orig/fs/mountfd.c	2004-10-22 17:17:40.736271288 -0400
>>+++ linux-2.6.9-quilt/fs/mountfd.c	2004-10-22 17:17:41.367175376 -0400
>>@@ -11,6 +11,8 @@
>> 
>> #define VFSMOUNT(filp) ((struct vfsmount *)((filp)->private_data))
>> 
>>+extern int do_umount(struct vfsmount *mnt, int flags);
>>+
>> static struct vfsmount *mfdfs_mnt;
>> 
>> static void mfdfs_read_inode(struct inode *inode);
>>@@ -72,6 +74,18 @@ static int mfd_release(struct inode *ino
>> 	return 0;
>> }
>> 
>>+static long mfd_umount(struct file *mountfilp, int flags)
>>+{
>>+	struct vfsmount *mnt;
>>+	int error;
>>+	
>>+	mnt = mntget(VFSMOUNT(mountfilp));
>>+
>>+	error = do_umount(mnt, flags);
>>+
>>+	return error;
>>+}
>>+
>> static int mfd_ioctl(struct inode *inode, struct file *filp,
>> 		     unsigned int cmd, unsigned long arg);
>> static struct file_operations mfd_file_ops = {
>>@@ -243,6 +257,12 @@ static int mfd_ioctl(struct inode *inode
>> 	switch (cmd) {
>> 	case MOUNTFD_IOC_GETDIRFD:
>> 		return mfd_getdirfd(filp);
>>+	case MOUNTFD_IOC_DETACH:
>>+		return mfd_umount(filp, MNT_DETACH);
>>+	case MOUNTFD_IOC_UNMOUNT:
>>+		return mfd_umount(filp, 0);
>>+	case MOUNTFD_IOC_FORCEDUNMOUNT:
>>+		return mfd_umount(filp, MNT_FORCE);
> 
> 
> Urgg, you don't want to add gazillions of strange ioctls, do you?
> 

Only a couple million ;)

I have toyed with different interfaces.  I have older patches that would
allow you to read/write on the fd to perform ops, but the code is a mess
of parsing/data checks.  I also toyed with a multiplexed syscall, but
realized real quick that it was an ioctl with a different name, that
only worked on mountfds.

ioctl ended up being the cleanest solution (I came up with) in the end.

Alternatives?

- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice

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