[PATCH 16/18] nfsd: switch nfsd4_create_file() to use vfs_lookup_open()

From: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>

Currently nfsd4_create_file() performs a lookup via start_creating() and
then if that reports a negative dentry it uses dentry_create() to create
the file.
dentry_create() will use ->atomic_open if available.  Part of the point
of supporting atomic_open is to avoid needing a separate lookup.
->atomic_open can do lookup, create, open all in one operation.  So
doing a lookup before dentry_create() is not optimal.

So change to use vfs_lookup_open() which combines lookup, create, and open,
either by using atomic_open or by calling the individual functions (but
not both).

This means that we don't need to lock that parent
(start_creating/end_creating).
We also don't need to get write-access (fh_want_write/fh_drop_write)
except in the unusual case of a read-only creating open.

Also we only set O_EXCL in the NFS4_CREATE_GUARDED case.  This the an
NFS protocol option which requests the server to take full
responsibility for atomic-create.  For NFS4_CREATE_EXCLUSIVE and
NFS4_CREATE_EXCLUSIVE4_1 the NFS protocol takes responsibilty for
exclusive create by providing a verifier to store with the file, and
using O_EXCL would interfere with this.

Signed-off-by: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>
---
 fs/nfsd/nfs4proc.c | 59 ++++++++++++++++------------------------------
 1 file changed, 20 insertions(+), 39 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 5bd19e5d9e34..61ecd4123817 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -219,14 +219,13 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		.na_seclabel	= &open->op_label,
 	};
 	int oflags = O_CREAT | O_LARGEFILE;
-	struct dentry *parent, *child = ERR_PTR(-EINVAL);
-	struct path path = {
+	struct dentry *child = ERR_PTR(-EINVAL);
+	struct path parent = {
 		.mnt = fhp->fh_export->ex_path.mnt,
+		.dentry = fhp->fh_dentry,
 	};
 	__u32 v_mtime, v_atime;
-	struct inode *inode;
 	__be32 status;
-	int host_err;
 
 	if (isdotent(open->op_fname, open->op_fnamelen))
 		return nfserr_exist;
@@ -236,10 +235,8 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	status = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC);
 	if (status != nfs_ok)
 		return status;
-	parent = fhp->fh_dentry;
-	inode = d_inode(parent);
 
-	if (!IS_POSIXACL(inode))
+	if (!IS_POSIXACL(d_inode(parent.dentry)))
 		iap->ia_mode &= ~current_umask();
 
 	if (!is_create_with_attrs(open)) {
@@ -287,9 +284,12 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		iap->ia_atime.tv_sec = v_atime;
 		iap->ia_mtime.tv_nsec = 0;
 		iap->ia_atime.tv_nsec = 0;
-
-		oflags |= O_EXCL;
 	}
+	/* Only ask the fs to provide exclusive-create if we aren't using
+	 * the NFS verifier to do it outselves.
+	 */
+	if (open->op_createmode == NFS4_CREATE_GUARDED)
+		oflags |= O_EXCL;
 
 	switch (open->op_share_access & NFS4_SHARE_ACCESS_BOTH) {
 	case NFS4_SHARE_ACCESS_WRITE:
@@ -302,33 +302,18 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		oflags |= O_RDONLY;
 	}
 
-	host_err = fh_want_write(fhp);
-	if (host_err)
-		return nfserrno(host_err);
-
-	child = start_creating(&nop_mnt_idmap, parent,
-			       &QSTR_LEN(open->op_fname, open->op_fnamelen));
-	if (IS_ERR(child)) {
-		status = nfserrno(PTR_ERR(child));
-		goto out_write;
-	}
-	path.dentry = child;
-
-	if (d_really_is_negative(child)) {
-		open->op_filp = dentry_create(&path, oflags, open->op_iattr.ia_mode,
-					      current_cred());
-		child = path.dentry;
-
-		if (IS_ERR(open->op_filp)) {
-			end_creating(child);
-			status = nfserrno(PTR_ERR(open->op_filp));
-			open->op_filp = NULL;
-			goto out_write;
-		}
-
-		open->op_created = open->op_filp->f_mode & FMODE_CREATED;
+	open->op_filp = vfs_lookup_open(&parent,
+					&QSTR_LEN(open->op_fname,
+						  open->op_fnamelen),
+					oflags,
+					open->op_iattr.ia_mode);
+	if (IS_ERR(open->op_filp)) {
+		status = nfserrno(PTR_ERR(open->op_filp));
+		open->op_filp = NULL;
+		goto out;
 	}
-	end_creating(child);
+	child = open->op_filp->f_path.dentry;
+	open->op_created = open->op_filp->f_mode & FMODE_CREATED;
 	fh_drop_write(fhp);
 
 	status = fh_compose(resfhp, fhp->fh_export, child, fhp);
@@ -397,10 +382,6 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 out:
 	nfsd_attrs_free(&attrs);
 	return status;
-
-out_write:
-	fh_drop_write(fhp);
-	goto out;
 }
 
 /**
-- 
2.50.0.107.gf914562f5916.dirty