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Subject[PATCH 16/16] nfs: don't open in ->d_revalidate
Date
From: Miklos Szeredi <mszeredi@suse.cz>

NFSv4 can't do reliable opens in d_revalidate, since it cannot know whether a
mount needs to be followed or not. It does check d_mountpoint() on the dentry,
which can result in a weird error if the VFS found that the mount does not in
fact need to be followed, e.g.:

# mount --bind /mnt/nfs /mnt/nfs-clone
# echo something > /mnt/nfs/tmp/bar
# echo x > /tmp/file
# mount --bind /tmp/file /mnt/nfs-clone/tmp/bar
# cat /mnt/nfs/tmp/bar
cat: /mnt/nfs/tmp/bar: Not a directory
Which should, by any sane filesystem, result in "something" being printed.

So instead do the open in f_op->open() and in the unlikely case that the cached
dentry turned out to be invalid, drop the dentry and return EOPENSTALE to let
the VFS retry.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: Trond Myklebust <Trond.Myklebust@netapp.com>
---
fs/nfs/dir.c | 56 +++-------------------------------------
fs/nfs/file.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 78 insertions(+), 55 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 4aaf031..10ce72e 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1328,10 +1328,10 @@ out:
}

#ifdef CONFIG_NFS_V4
-static int nfs_open_revalidate(struct dentry *, struct nameidata *);
+static int nfs4_lookup_revalidate(struct dentry *, struct nameidata *);

const struct dentry_operations nfs4_dentry_operations = {
- .d_revalidate = nfs_open_revalidate,
+ .d_revalidate = nfs4_lookup_revalidate,
.d_delete = nfs_dentry_delete,
.d_iput = nfs_dentry_iput,
.d_automount = nfs_d_automount,
@@ -1493,13 +1493,11 @@ no_open:
return nfs_lookup(dir, dentry, nd);
}

-static int nfs_open_revalidate(struct dentry *dentry, struct nameidata *nd)
+static int nfs4_lookup_revalidate(struct dentry *dentry, struct nameidata *nd)
{
struct dentry *parent = NULL;
struct inode *inode;
struct inode *dir;
- struct nfs_open_context *ctx;
- struct iattr attr;
int openflags, ret = 0;

if (nd->flags & LOOKUP_RCU)
@@ -1528,57 +1526,13 @@ static int nfs_open_revalidate(struct dentry *dentry, struct nameidata *nd)
/* We cannot do exclusive creation on a positive dentry */
if ((openflags & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
goto no_open_dput;
- /* We can't create new files here */
- openflags &= ~(O_CREAT|O_EXCL);
-
- ctx = create_nfs_open_context(dentry, openflags);
- ret = PTR_ERR(ctx);
- if (IS_ERR(ctx))
- goto out;

- attr.ia_valid = 0;
- if (openflags & O_TRUNC) {
- attr.ia_valid |= ATTR_SIZE;
- attr.ia_size = 0;
- nfs_wb_all(inode);
- }
-
- /*
- * Note: we're not holding inode->i_mutex and so may be racing with
- * operations that change the directory. We therefore save the
- * change attribute *before* we do the RPC call.
- */
- inode = NFS_PROTO(dir)->open_context(dir, ctx, openflags, &attr);
- if (IS_ERR(inode)) {
- ret = PTR_ERR(inode);
- switch (ret) {
- case -EPERM:
- case -EACCES:
- case -EDQUOT:
- case -ENOSPC:
- case -EROFS:
- goto out_put_ctx;
- default:
- goto out_drop;
- }
- }
- iput(inode);
- if (inode != dentry->d_inode)
- goto out_drop;
+ /* Let f_op->open() actually open (and revalidate) the file */
+ ret = 1;

- nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
- ret = nfs_intent_set_file(nd, ctx);
- if (ret >= 0)
- ret = 1;
out:
dput(parent);
return ret;
-out_drop:
- d_drop(dentry);
- ret = 0;
-out_put_ctx:
- put_nfs_open_context(ctx);
- goto out;

no_open_dput:
dput(parent);
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index aa9b709..92268bf 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -871,12 +871,81 @@ const struct file_operations nfs_file_operations = {
static int
nfs4_file_open(struct inode *inode, struct file *filp)
{
+ struct nfs_open_context *ctx;
+ struct dentry *dentry = filp->f_path.dentry;
+ struct dentry *parent = NULL;
+ struct inode *dir;
+ unsigned openflags = filp->f_flags;
+ struct iattr attr;
+ int err;
+
+ BUG_ON(inode != dentry->d_inode);
/*
- * NFSv4 opens are handled in d_lookup and d_revalidate. If we get to
- * this point, then something is very wrong
+ * If no cached dentry exists or if it's negative, NFSv4 handled the
+ * opens in ->lookup() or ->create().
+ *
+ * We only get this far for a cached positive dentry. We skipped
+ * revalidation, so handle it here by dropping the dentry and returning
+ * -EOPENSTALE. The VFS will retry the lookup/create/open.
*/
- dprintk("NFS: %s called! inode=%p filp=%p\n", __func__, inode, filp);
- return -ENOTDIR;
+
+ dprintk("NFS: open file(%s/%s)\n",
+ dentry->d_parent->d_name.name,
+ dentry->d_name.name);
+
+ if ((openflags & O_ACCMODE) == 3)
+ openflags--;
+
+ /* We can't create new files here */
+ openflags &= ~(O_CREAT|O_EXCL);
+
+ parent = dget_parent(dentry);
+ dir = parent->d_inode;
+
+ ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
+ err = PTR_ERR(ctx);
+ if (IS_ERR(ctx))
+ goto out;
+
+ attr.ia_valid = 0;
+ if (openflags & O_TRUNC) {
+ attr.ia_valid |= ATTR_SIZE;
+ attr.ia_size = 0;
+ nfs_wb_all(inode);
+ }
+
+ inode = NFS_PROTO(dir)->open_context(dir, ctx, openflags, &attr);
+ if (IS_ERR(inode)) {
+ err = PTR_ERR(inode);
+ switch (err) {
+ case -EPERM:
+ case -EACCES:
+ case -EDQUOT:
+ case -ENOSPC:
+ case -EROFS:
+ goto out_put_ctx;
+ default:
+ goto out_drop;
+ }
+ }
+ iput(inode);
+ if (inode != dentry->d_inode)
+ goto out_drop;
+
+ nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+ nfs_file_set_open_context(filp, ctx);
+ err = 0;
+
+out_put_ctx:
+ put_nfs_open_context(ctx);
+out:
+ dput(parent);
+ return err;
+
+out_drop:
+ d_drop(dentry);
+ err = -EOPENSTALE;
+ goto out_put_ctx;
}

const struct file_operations nfs4_file_operations = {
--
1.7.7


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