Commit 64894cf8 authored by Al Viro's avatar Al Viro
Browse files

simplify lookup_open()/atomic_open() - do the temporary mnt_want_write() early 



The write ref to vfsmount taken in lookup_open()/atomic_open() is going to
be dropped; we take the one to stay in dentry_open().  Just grab the temporary
in caller if it looks like we are going to need it (create/truncate/writable open)
and pass (by value) "has it succeeded" flag.  Instead of doing mnt_want_write()
inside, check that flag and treat "false" as "mnt_want_write() has just failed".
mnt_want_write() is cheap and the things get considerably simpler and more robust
that way - we get it and drop it in the same function, to start with, rather
than passing a "has something in the guts of really scary functions taken it"
back to caller.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent f8310c59

fs/namei.c

+29 −22
Original line number Diff line number Diff line
@@ -2395,7 +2395,7 @@ static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode) 
static int atomic_open(struct nameidata *nd, struct dentry *dentry,

			struct path *path, struct file *file,

			const struct open_flags *op,

			bool *want_write, bool need_lookup,

			bool got_write, bool need_lookup,

			int *opened)

{

	struct inode *dir =  nd->path.dentry->d_inode;
@@ -2432,12 +2432,9 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry, 
	 * Another problem is returing the "right" error value (e.g. for an

	 * O_EXCL open we want to return EEXIST not EROFS).

	 */

	if ((open_flag & (O_CREAT | O_TRUNC)) ||

	    (open_flag & O_ACCMODE) != O_RDONLY) {

		error = mnt_want_write(nd->path.mnt);

		if (!error) {

			*want_write = true;

		} else if (!(open_flag & O_CREAT)) {

	if (((open_flag & (O_CREAT | O_TRUNC)) ||

	    (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) {

		if (!(open_flag & O_CREAT)) {

			/*

			 * No O_CREATE -> atomicity not a requirement -> fall

			 * back to lookup + open
@@ -2445,11 +2442,11 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry, 
			goto no_open;

		} else if (open_flag & (O_EXCL | O_TRUNC)) {

			/* Fall back and fail with the right error */

			create_error = error;

			create_error = -EROFS;

			goto no_open;

		} else {

			/* No side effects, safe to clear O_CREAT */

			create_error = error;

			create_error = -EROFS;

			open_flag &= ~O_CREAT;

		}

	}
@@ -2556,7 +2553,7 @@ looked_up: 
static int lookup_open(struct nameidata *nd, struct path *path,

			struct file *file,

			const struct open_flags *op,

			bool *want_write, int *opened)

			bool got_write, int *opened)

{

	struct dentry *dir = nd->path.dentry;

	struct inode *dir_inode = dir->d_inode;
@@ -2574,7 +2571,7 @@ static int lookup_open(struct nameidata *nd, struct path *path, 
		goto out_no_open;



	if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {

		return atomic_open(nd, dentry, path, file, op, want_write,

		return atomic_open(nd, dentry, path, file, op, got_write,

				   need_lookup, opened);

	}
@@ -2598,10 +2595,10 @@ static int lookup_open(struct nameidata *nd, struct path *path, 
		 * a permanent write count is taken through

		 * the 'struct file' in finish_open().

		 */

		error = mnt_want_write(nd->path.mnt);

		if (error)

		if (!got_write) {

			error = -EROFS;

			goto out_dput;

		*want_write = true;

		}

		*opened |= FILE_CREATED;

		error = security_path_mknod(&nd->path, dentry, mode, 0);

		if (error)
@@ -2631,7 +2628,7 @@ static int do_last(struct nameidata *nd, struct path *path, 
	struct dentry *dir = nd->path.dentry;

	int open_flag = op->open_flag;

	bool will_truncate = (open_flag & O_TRUNC) != 0;

	bool want_write = false;

	bool got_write = false;

	int acc_mode = op->acc_mode;

	struct inode *inode;

	bool symlink_ok = false;
@@ -2700,8 +2697,18 @@ static int do_last(struct nameidata *nd, struct path *path, 
	}



retry_lookup:

	if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {

		error = mnt_want_write(nd->path.mnt);

		if (!error)

			got_write = true;

		/*

		 * do _not_ fail yet - we might not need that or fail with

		 * a different error; let lookup_open() decide; we'll be

		 * dropping this one anyway.

		 */

	}

	mutex_lock(&dir->d_inode->i_mutex);

	error = lookup_open(nd, path, file, op, &want_write, opened);

	error = lookup_open(nd, path, file, op, got_write, opened);

	mutex_unlock(&dir->d_inode->i_mutex);



	if (error <= 0) {
@@ -2736,9 +2743,9 @@ retry_lookup: 
	 * possible mount and symlink following (this might be optimized away if

	 * necessary...)

	 */

	if (want_write) {

	if (got_write) {

		mnt_drop_write(nd->path.mnt);

		want_write = false;

		got_write = false;

	}



	error = -EEXIST;
@@ -2803,7 +2810,7 @@ finish_open: 
		error = mnt_want_write(nd->path.mnt);

		if (error)

			goto out;

		want_write = true;

		got_write = true;

	}

finish_open_created:

	error = may_open(&nd->path, acc_mode, open_flag);
@@ -2830,7 +2837,7 @@ opened: 
			goto exit_fput;

	}

out:

	if (want_write)

	if (got_write)

		mnt_drop_write(nd->path.mnt);

	path_put(&save_parent);

	terminate_walk(nd);
@@ -2854,9 +2861,9 @@ stale_open: 
	nd->inode = dir->d_inode;

	save_parent.mnt = NULL;

	save_parent.dentry = NULL;

	if (want_write) {

	if (got_write) {

		mnt_drop_write(nd->path.mnt);

		want_write = false;

		got_write = false;

	}

	retried = true;

	goto retry_lookup;

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