Commit 7c6c5249 authored by NeilBrown's avatar NeilBrown Committed by Trond Myklebust
Browse files

NFS: add atomic_open for NFSv3 to handle O_TRUNC correctly. 



With two clients, each with NFSv3 mounts of the same directory, the sequence:

   client1            client2
  ls -l afile
                      echo hello there > afile
  echo HELLO > afile
  cat afile

will show
   HELLO
   there

because the O_TRUNC requested in the final 'echo' doesn't take effect.
This is because the "Negative dentry, just create a file" section in
lookup_open() assumes that the file *does* get created since the dentry
was negative, so it sets FMODE_CREATED, and this causes do_open() to
clear O_TRUNC and so the file doesn't get truncated.

Even mounting with -o lookupcache=none does not help as
nfs_neg_need_reval() always returns false if LOOKUP_CREATE is set.

This patch fixes the problem by providing an atomic_open inode operation
for NFSv3 (and v2).  The code is largely the code from the branch in
lookup_open() when atomic_open is not provided.  The significant change
is that the O_TRUNC flag is passed a new nfs_do_create() which add
'trunc' handling to nfs_create().

With this change we also optimise away an unnecessary LOOKUP before the
file is created.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
parent 464b424f

fs/nfs/dir.c

+51 −3
Original line number Diff line number Diff line
@@ -56,6 +56,8 @@ static int nfs_readdir(struct file *, struct dir_context *); 
static int nfs_fsync_dir(struct file *, loff_t, loff_t, int);

static loff_t nfs_llseek_dir(struct file *, loff_t, int);

static void nfs_readdir_clear_array(struct folio *);

static int nfs_do_create(struct inode *dir, struct dentry *dentry,

			 umode_t mode, int open_flags);



const struct file_operations nfs_dir_operations = {

	.llseek		= nfs_llseek_dir,
@@ -2243,6 +2245,41 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags) 


#endif /* CONFIG_NFSV4 */



int nfs_atomic_open_v23(struct inode *dir, struct dentry *dentry,

			struct file *file, unsigned int open_flags,

			umode_t mode)

{



	/* Same as look+open from lookup_open(), but with different O_TRUNC

	 * handling.

	 */

	int error = 0;



	if (open_flags & O_CREAT) {

		file->f_mode |= FMODE_CREATED;

		error = nfs_do_create(dir, dentry, mode, open_flags);

		if (error)

			return error;

		return finish_open(file, dentry, NULL);

	} else if (d_in_lookup(dentry)) {

		/* The only flags nfs_lookup considers are

		 * LOOKUP_EXCL and LOOKUP_RENAME_TARGET, and

		 * we want those to be zero so the lookup isn't skipped.

		 */

		struct dentry *res = nfs_lookup(dir, dentry, 0);



		d_lookup_done(dentry);

		if (unlikely(res)) {

			if (IS_ERR(res))

				return PTR_ERR(res);

			return finish_no_open(file, res);

		}

	}

	return finish_no_open(file, NULL);



}

EXPORT_SYMBOL_GPL(nfs_atomic_open_v23);



struct dentry *

nfs_add_or_obtain(struct dentry *dentry, struct nfs_fh *fhandle,

				struct nfs_fattr *fattr)
@@ -2303,18 +2340,23 @@ EXPORT_SYMBOL_GPL(nfs_instantiate); 
 * that the operation succeeded on the server, but an error in the

 * reply path made it appear to have failed.

 */

int nfs_create(struct mnt_idmap *idmap, struct inode *dir,

	       struct dentry *dentry, umode_t mode, bool excl)

static int nfs_do_create(struct inode *dir, struct dentry *dentry,

			 umode_t mode, int open_flags)

{

	struct iattr attr;

	int open_flags = excl ? O_CREAT | O_EXCL : O_CREAT;

	int error;



	open_flags |= O_CREAT;



	dfprintk(VFS, "NFS: create(%s/%lu), %pd\n",

			dir->i_sb->s_id, dir->i_ino, dentry);



	attr.ia_mode = mode;

	attr.ia_valid = ATTR_MODE;

	if (open_flags & O_TRUNC) {

		attr.ia_size = 0;

		attr.ia_valid |= ATTR_SIZE;

	}



	trace_nfs_create_enter(dir, dentry, open_flags);

	error = NFS_PROTO(dir)->create(dir, dentry, &attr, open_flags);
@@ -2326,6 +2368,12 @@ int nfs_create(struct mnt_idmap *idmap, struct inode *dir, 
	d_drop(dentry);

	return error;

}



int nfs_create(struct mnt_idmap *idmap, struct inode *dir,

	       struct dentry *dentry, umode_t mode, bool excl)

{

	return nfs_do_create(dir, dentry, mode, excl ? O_EXCL : 0);

}

EXPORT_SYMBOL_GPL(nfs_create);



/*

fs/nfs/nfs3proc.c

+1 −0
Original line number Diff line number Diff line
@@ -986,6 +986,7 @@ static int nfs3_have_delegation(struct inode *inode, fmode_t flags) 


static const struct inode_operations nfs3_dir_inode_operations = {

	.create		= nfs_create,

	.atomic_open	= nfs_atomic_open_v23,

	.lookup		= nfs_lookup,

	.link		= nfs_link,

	.unlink		= nfs_unlink,

fs/nfs/proc.c

+1 −0
Original line number Diff line number Diff line
@@ -695,6 +695,7 @@ static int nfs_have_delegation(struct inode *inode, fmode_t flags) 
static const struct inode_operations nfs_dir_inode_operations = {

	.create		= nfs_create,

	.lookup		= nfs_lookup,

	.atomic_open	= nfs_atomic_open_v23,

	.link		= nfs_link,

	.unlink		= nfs_unlink,

	.symlink	= nfs_symlink,

include/linux/nfs_fs.h

+3 −0
Original line number Diff line number Diff line
@@ -561,6 +561,9 @@ extern int nfs_may_open(struct inode *inode, const struct cred *cred, int openfl 
extern void nfs_access_zap_cache(struct inode *inode);

extern int nfs_access_get_cached(struct inode *inode, const struct cred *cred,

				 u32 *mask, bool may_block);

extern int nfs_atomic_open_v23(struct inode *dir, struct dentry *dentry,

			       struct file *file, unsigned int open_flags,

			       umode_t mode);



/*

 * linux/fs/nfs/symlink.c