Re: Drop dcache entry after creating snapshot and subvolume
On Wednesday 28 May 2008, Christoph Hellwig wrote: On Wed, May 28, 2008 at 12:41:24AM +0200, Sven Wegener wrote: I have a patch (see below) that does an explicit d_drop() on the dentry after looking it up via d_find_alias() and d_lookup(), starting at the root inode. Currently it's for snapshot creation only, subvolume creation needs the same. There doesn't seem to be a kernel function for this case and using the normal d_revalidate method is inefficient as snapshot and subvolume creation is the only place where we need this and the creation is a rare case. Is this the right way to go? I don't like this manual dropping very much. Rather the snapshot should be created using vfs_mkdir or equivalent opencoded bits that actually turn the negative dentry into the real instanciated one. Then again it might actually be better to have a separate superblock for the snapshot to not get a too messy dentry tree, but before commenting on that I need to actually dig into that area of btrfs again. There's a looming dentry mess with snapshot deletion, where I want to be able to delete a snapshot or subvolume by efficiently walking the btree, but I first need to find any dentries (with the same semantics as unmount). But, I don't think it makes sense to give each subvolume its own super, there's too much shared between them (even btree blocks). Also, today all the subvolumes and snapshots live in the root directory, but the long term setup will have a real directory tree there, and so we need to make directory operations for that btree. But for today, I think Sven's patch is a good idea. -chris -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Drop dcache entry after creating snapshot and subvolume
Hi all,
when creating a new snapshot or subvolume we need to drop an existing
negative dentry for the new name, else this happens:
host ~ # ls -l /mnt/btrfs
total 1
dr-xr-xr-x 1 root root 0 Jan 1 1970 default
host ~ # stat /mnt/btrfs/snapshot
stat: cannot stat `/mnt/btrfs/snapshot': No such file or directory
host ~ # btrfsctl -s snapshot /mnt/btrfs/default
ioctl returns 0
host ~ # stat /mnt/btrfs/snapshot
stat: cannot stat `/mnt/btrfs/snapshot': No such file or directory
host ~ # ls -l /mnt/btrfs
ls: cannot access /mnt/btrfs/snapshot: No such file or directory
total 1
dr-xr-xr-x 1 root root 0 Jan 1 1970 default
d? ? ???? snapshot
I have a patch (see below) that does an explicit d_drop() on the dentry
after looking it up via d_find_alias() and d_lookup(), starting at the
root inode. Currently it's for snapshot creation only, subvolume creation
needs the same. There doesn't seem to be a kernel function for this case
and using the normal d_revalidate method is inefficient as snapshot and
subvolume creation is the only place where we need this and the creation
is a rare case. Is this the right way to go?
Sven
---
transaction.c | 18 ++
1 file changed, 18 insertions(+)
--- a/transaction.c
+++ b/transaction.c
@@ -557,6 +557,8 @@
struct btrfs_root *tree_root = fs_info-tree_root;
struct btrfs_root *root = pending-root;
struct extent_buffer *tmp;
+ struct dentry *alias, *snap;
+ struct qstr qstr;
int ret;
u64 objectid;
@@ -604,6 +606,22 @@
ret = btrfs_insert_inode_ref(trans, root-fs_info-tree_root,
pending-name, strlen(pending-name), objectid,
root-fs_info-sb-s_root-d_inode-i_ino);
+
+ /*
+* We need to drop the dcache entry for the new snapshot.
+*/
+ alias = d_find_alias(root-fs_info-sb-s_root-d_inode);
+ if (alias) {
+ qstr.name = pending-name;
+ qstr.len = strlen(qstr.name);
+ qstr.hash = full_name_hash(qstr.name, qstr.len);
+ snap = d_lookup(alias, qstr);
+ dput(alias);
+ if (snap) {
+ d_drop(snap);
+ dput(snap);
+ }
+ }
fail:
kfree(new_root_item);
return ret;
--
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Re: Drop dcache entry after creating snapshot and subvolume
On Wed, May 28, 2008 at 12:41:24AM +0200, Sven Wegener wrote: I have a patch (see below) that does an explicit d_drop() on the dentry after looking it up via d_find_alias() and d_lookup(), starting at the root inode. Currently it's for snapshot creation only, subvolume creation needs the same. There doesn't seem to be a kernel function for this case and using the normal d_revalidate method is inefficient as snapshot and subvolume creation is the only place where we need this and the creation is a rare case. Is this the right way to go? I don't like this manual dropping very much. Rather the snapshot should be created using vfs_mkdir or equivalent opencoded bits that actually turn the negative dentry into the real instanciated one. Then again it might actually be better to have a separate superblock for the snapshot to not get a too messy dentry tree, but before commenting on that I need to actually dig into that area of btrfs again. -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
