Re: [PATCH 2/3] NFS support for btrfs - v2

David Woodhouse
2008-08-13T08:53:17Z

On Tue, 2008-08-12 at 14:51 -0400, Christoph Hellwig wrote:
> On Tue, Aug 12, 2008 at 02:46:46PM +0100, David Woodhouse wrote:
> > +static inline struct dentry *d_obtain_alias(struct inode *inode)
> > +{
> > + struct dentry *d = d_alloc_anon(inode);
> > + if (!d)
> > + iput(inode);
> > + return d;
> > +}
> > +#endif
>
> I'm not sure when al wants to merge with Linus, but the for-next naming
> makes it sound like the tree is the .28 queue. Also please take the
> full implementation of d_obtain_alias from
>
> http://git.kernel.org/?p=linux/kernel/git/viro/vfs-2.6.git;a=commitdiff;h=10cdb734be3c4175b977ba18eafbaba8e5716291
>
> please. Your light implementation will crash and burn when btrfs_iget
> returns an error.

Well spotted; thanks.

> > +/* The size of encoded fh is the type number of the fh itself */
> > +#define BTRFS_FID_NON_CONNECTABLE 5
> > +#define BTRFS_FID_CONNECTABLE 8
>
> That was an assumption in the very old code, but I think it's a very
> bad idea. Just give your filehandles a uniqueue type number, e.g. in
> the 0x4? range so that people looking at nfs traffic using a packet
> analyzer know what kind of fhs they are actually dealing with.

Ok, I'll submit the patch to include/linux/exportfs.h separately -- the
numbers might as well be reserved immediately.

Btw, I'm not convinced nfsd does the right thing when we return 255 from
->encode_fh(). It seems to leak a refcount somewhere in nfs code, so I
can't stop the server and can't unmount the file system.

> > + if (IS_ERR(inode))
> > + return (void *)inode;
> > +
> > + if (generation != inode->i_generation) {
> > + iput(inode);
> > + return ERR_PTR(-ESTALE);
> > + }
> > +
> > + result = d_alloc_anon(inode);
> > + if (!result) {
> > + iput(inode);
> > + return ERR_PTR(-ENOMEM);
> > + }
>
> Didn't you intend to use d_obtain_alias?

Oops, yes. I did use it once; I missed the second one though.

I'll merge this into the patch in question...

diff --git a/compat.h b/compat.h
index 1040f07..d45fb37 100644
--- a/compat.h
+++ b/compat.h
@@ -8,7 +8,14 @@
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,27)
static inline struct dentry *d_obtain_alias(struct inode *inode)
{
- struct dentry *d = d_alloc_anon(inode);
+ struct dentry *d;
+
+ if (!inode)
+ return NULL;
+ if (IS_ERR(inode))
+ return ERR_CAST(inode);
+
+ d = d_alloc_anon(inode);
if (!d)
iput(inode);
return d;
diff --git a/export.c b/export.c
index 253080a..34e4631 100644
--- a/export.c
+++ b/export.c
@@ -7,9 +7,13 @@
#include "export.h"
#include "compat.h"

-/* The size of encoded fh is the type number of the fh itself */
-#define BTRFS_FID_NON_CONNECTABLE 5
-#define BTRFS_FID_CONNECTABLE 8
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,28)
+#define FILEID_BTRFS_WITHOUT_PARENT 0x4e
+#define FILEID_BTRFS_WITH_PARENT 0x4f
+#endif
+
+#define BTRFS_FID_SIZE_NON_CONNECTABLE (offsetof(struct btrfs_fid, parent_objectid)/4)
+#define BTRFS_FID_SIZE_CONNECTABLE (sizeof(struct btrfs_fid)/4)

static int btrfs_encode_fh(struct dentry *dentry, u32 *fh, int *max_len,
int connectable)
@@ -17,12 +21,14 @@ static int btrfs_encode_fh(struct dentry *dentry, u32 *fh, int *max_len,
struct btrfs_fid *fid = (struct btrfs_fid *)fh;
struct inode *inode = dentry->d_inode;
int len = *max_len;
+ int type;

- if ((len < BTRFS_FID_NON_CONNECTABLE) ||
- (connectable && len < BTRFS_FID_CONNECTABLE))
+ if ((len < BTRFS_FID_SIZE_NON_CONNECTABLE) ||
+ (connectable && len < BTRFS_FID_SIZE_CONNECTABLE))
return 255;

- len = BTRFS_FID_NON_CONNECTABLE;
+ len = BTRFS_FID_SIZE_NON_CONNECTABLE;
+ type = FILEID_BTRFS_WITHOUT_PARENT;

fid->objectid = BTRFS_I(inode)->location.objectid;
fid->root_objectid = BTRFS_I(inode)->root->objectid;
@@ -38,13 +44,12 @@ static int btrfs_encode_fh(struct dentry *dentry, u32 *fh, int *max_len,
fid->parent_gen = parent->i_generation;

spin_unlock(&dentry->d_lock);
- len = BTRFS_FID_CONNECTABLE;
+ len = BTRFS_FID_SIZE_CONNECTABLE;
+ type = FILEID_BTRFS_WITH_PARENT;
}
- *max_len = len;
-
- /* We return length itself for the type */
- return len;

+ *max_len = len;
+ return type;
}

static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
@@ -69,11 +74,9 @@ static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
return ERR_PTR(-ESTALE);
}

- result = d_alloc_anon(inode);
- if (!result) {
- iput(inode);
+ result = d_obtain_alias(inode);
+ if (!result)
return ERR_PTR(-ENOMEM);
- }

return result;
}
@@ -85,7 +88,8 @@ static struct dentry *btrfs_fh_to_parent(struct super_block *sb, struct fid *fh,
u64 objectid, root_objectid;
u32 generation;

- if (fh_type != BTRFS_FID_CONNECTABLE)
+ if (fh_type != FILEID_BTRFS_WITH_PARENT ||
+ fh_len != BTRFS_FID_SIZE_CONNECTABLE)
return NULL;

root_objectid = fid->root_objectid;
@@ -102,7 +106,10 @@ static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
u64 objectid, root_objectid;
u32 generation;

- if (fh_type > BTRFS_FID_CONNECTABLE)
+ if ((fh_type != FILEID_BTRFS_WITH_PARENT ||
+ fh_len != BTRFS_FID_SIZE_CONNECTABLE) &&
+ (fh_type != FILEID_BTRFS_WITHOUT_PARENT ||
+ fh_len != BTRFS_FID_SIZE_NON_CONNECTABLE))
return NULL;

objectid = fid->objectid;

--
David Woodhouse Open Source Technology Centre
David.Woodhouse@intel.com Intel Corporation