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

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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: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2012-07-31 00:53:35 +04:00
parent f8310c5920
commit 64894cf843
1 changed files with 29 additions and 22 deletions
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51
fs/namei.c
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@ -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;