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Subject[PATCH] lazy umount (4/4)
Part 4/4:
Lazy umount itself. New functions - next_mnt() (walks the vfsmount
tree) and umount_tree() (detach all mounts in a subtree and do mntput() on
each vfsmonut there). do_umount() reorganized to use umount_tree() (if
vfsmount is not busy, it can't have anything mounted on it, so umount_tree()
does the right thing). New flag to umount(2) - MNT_DETACH. With that
flag we call umount_tree() even if vfsmount is busy - i.e. we undo all
mounts in a subtree and drop the references that pin vfsmounts down.
As soon as they are not busy they will be deactivated (by mntput()).

diff -urN S10-pre9-check_mnt/fs/super.c S10-pre9-lazy_umount/fs/super.c
--- S10-pre9-check_mnt/fs/super.c Fri Sep 14 14:04:01 2001
+++ S10-pre9-lazy_umount/fs/super.c Fri Sep 14 14:04:28 2001
@@ -356,6 +356,22 @@
nd->dentry->d_mounted++;
}

+static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
+{
+ struct list_head *next = p->mnt_mounts.next;
+ if (next == &p->mnt_mounts) {
+ while (1) {
+ if (p == root)
+ return NULL;
+ next = p->mnt_child.next;
+ if (next != &p->mnt_parent->mnt_mounts)
+ break;
+ p = p->mnt_parent;
+ }
+ }
+ return list_entry(next, struct vfsmount, mnt_child);
+}
+
static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root)
{
char *name = old->mnt_devname;
@@ -1124,10 +1140,52 @@
return 0;
}

+void umount_tree(struct vfsmount *mnt)
+{
+ struct vfsmount *p;
+ LIST_HEAD(kill);
+
+ if (list_empty(&mnt->mnt_list))
+ return;
+
+ for (p = mnt; p; p = next_mnt(p, mnt)) {
+ list_del(&p->mnt_list);
+ list_add(&p->mnt_list, &kill);
+ }
+
+ while (!list_empty(&kill)) {
+ mnt = list_entry(kill.next, struct vfsmount, mnt_list);
+ list_del_init(&mnt->mnt_list);
+ if (mnt->mnt_parent == mnt) {
+ spin_unlock(&dcache_lock);
+ } else {
+ struct nameidata old_nd;
+ detach_mnt(mnt, &old_nd);
+ spin_unlock(&dcache_lock);
+ path_release(&old_nd);
+ }
+ mntput(mnt);
+ spin_lock(&dcache_lock);
+ }
+}
+
static int do_umount(struct vfsmount *mnt, int flags)
{
struct super_block * sb = mnt->mnt_sb;
- struct nameidata parent_nd;
+ int retval = 0;
+
+ /*
+ * If we may have to abort operations to get out of this
+ * mount, and they will themselves hold resources we must
+ * allow the fs to do things. In the Unix tradition of
+ * 'Gee thats tricky lets do it in userspace' the umount_begin
+ * might fail to complete on the first run through as other tasks
+ * must return, and the like. Thats for the mount program to worry
+ * about for the moment.
+ */
+
+ if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
+ sb->s_op->umount_begin(sb);

/*
* No sense to grab the lock for this test, but test itself looks
@@ -1139,7 +1197,7 @@
* /reboot - static binary that would close all descriptors and
* call reboot(9). Then init(8) could umount root and exec /reboot.
*/
- if (mnt == current->fs->rootmnt) {
+ if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
int retval = 0;
/*
* Special case for "unmounting" root ...
@@ -1155,57 +1213,20 @@

spin_lock(&dcache_lock);

- if (atomic_read(&sb->s_active) > 1) {
- if (atomic_read(&mnt->mnt_count) > 2) {
- spin_unlock(&dcache_lock);
- return -EBUSY;
- }
- detach_mnt(mnt, &parent_nd);
- list_del(&mnt->mnt_list);
+ if (atomic_read(&sb->s_active) == 1) {
+ /* last instance - try to be smart */
spin_unlock(&dcache_lock);
- mntput(mnt);
- path_release(&parent_nd);
- return 0;
+ DQUOT_OFF(sb);
+ acct_auto_close(sb->s_dev);
+ spin_lock(&dcache_lock);
}
- spin_unlock(&dcache_lock);
-
- /*
- * Before checking whether the filesystem is still busy,
- * make sure the kernel doesn't hold any quota files open
- * on the device. If the umount fails, too bad -- there
- * are no quotas running any more. Just turn them on again.
- */
- DQUOT_OFF(sb);
- acct_auto_close(sb->s_dev);
-
- /*
- * If we may have to abort operations to get out of this
- * mount, and they will themselves hold resources we must
- * allow the fs to do things. In the Unix tradition of
- * 'Gee thats tricky lets do it in userspace' the umount_begin
- * might fail to complete on the first run through as other tasks
- * must return, and the like. Thats for the mount program to worry
- * about for the moment.
- */
-
- if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
- sb->s_op->umount_begin(sb);
-
- /* Something might grab it again - redo checks */
-
- spin_lock(&dcache_lock);
- if (atomic_read(&mnt->mnt_count) > 2) {
- spin_unlock(&dcache_lock);
- return -EBUSY;
+ retval = -EBUSY;
+ if (atomic_read(&mnt->mnt_count) == 2 || flags & MNT_DETACH) {
+ umount_tree(mnt);
+ retval = 0;
}
-
- /* OK, that's the point of no return */
- detach_mnt(mnt, &parent_nd);
- list_del(&mnt->mnt_list);
spin_unlock(&dcache_lock);
- mntput(mnt);
- path_release(&parent_nd);
- return 0;
+ return retval;
}

/*
diff -urN S10-pre9-check_mnt/include/linux/fs.h S10-pre9-lazy_umount/include/linux/fs.h
--- S10-pre9-check_mnt/include/linux/fs.h Fri Sep 14 12:58:46 2001
+++ S10-pre9-lazy_umount/include/linux/fs.h Fri Sep 14 14:04:28 2001
@@ -635,6 +635,7 @@
*/

#define MNT_FORCE 0x00000001 /* Attempt to forcibily umount */
+#define MNT_DETACH 0x00000002 /* Just detach from the tree */

#include <linux/minix_fs_sb.h>
#include <linux/ext2_fs_sb.h>

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