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SubjectRe: [RFC] atomic create+open
From
Date
on den 12.10.2005 Klokka 15:52 (+0200) skreiv Miklos Szeredi:

> > I don't care either way since we will not be supporting non-intent based
> > opens for NFSv4.
>
> I need this for FUSE, since non-create opens and non-exclusive open of
> positive dentry will be done through ->open().

How about something like the following instead? That gives you the
option of choosing a non-standard initialisation for the intent case,
with the default being ->open().

Cheers,
Trond
VFS: Allow the filesystem to return a full file pointer on open intent

This is needed by NFSv4 for atomicity reasons: our open command is in
fact a lookup+open, so we need to be able to propagate open context
information from lookup() into the resulting struct file's
private_data field.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---
fs/exec.c | 12 +++---
fs/namei.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++----
fs/open.c | 79 ++++++++++++++++++++++++++++++++++--------
include/linux/namei.h | 8 ++++
4 files changed, 165 insertions(+), 27 deletions(-)
Index: linux-2.6.14-rc4/fs/namei.c
===================================================================
--- linux-2.6.14-rc4.orig/fs/namei.c
+++ linux-2.6.14-rc4/fs/namei.c
@@ -28,6 +28,7 @@
#include <linux/syscalls.h>
#include <linux/mount.h>
#include <linux/audit.h>
+#include <linux/file.h>
#include <asm/namei.h>
#include <asm/uaccess.h>

@@ -317,6 +318,18 @@ void path_release_on_umount(struct namei
mntput_no_expire(nd->mnt);
}

+/**
+ * release_open_intent - free up open intent resources
+ * @nd: pointer to nameidata
+ */
+void release_open_intent(struct nameidata *nd)
+{
+ if (nd->intent.open.file->f_dentry == NULL)
+ put_filp(nd->intent.open.file);
+ else
+ fput(nd->intent.open.file);
+}
+
/*
* Internal lookup() using the new generic dcache.
* SMP-safe
@@ -1052,6 +1065,70 @@ out:
return retval;
}

+static int __path_lookup_intent_open(const char *name, unsigned int lookup_flags,
+ struct nameidata *nd, int open_flags, int create_mode)
+{
+ struct file *filp = get_empty_filp();
+ int err;
+
+ if (filp == NULL)
+ return -ENFILE;
+ nd->intent.open.file = filp;
+ nd->intent.open.flags = open_flags;
+ nd->intent.open.create_mode = create_mode;
+ err = path_lookup(name, lookup_flags|LOOKUP_OPEN, nd);
+ if (IS_ERR(nd->intent.open.file)) {
+ if (err == 0) {
+ err = PTR_ERR(nd->intent.open.file);
+ path_release(nd);
+ }
+ } else if (err != 0)
+ release_open_intent(nd);
+ return err;
+}
+
+/**
+ * path_lookup_open - lookup a file path with open intent
+ * @name: pointer to file name
+ * @lookup_flags: lookup intent flags
+ * @nd: pointer to nameidata
+ * @open_flags: open intent flags
+ */
+int path_lookup_open(const char *name, unsigned int lookup_flags,
+ struct nameidata *nd, int open_flags)
+{
+ return __path_lookup_intent_open(name, lookup_flags, nd,
+ open_flags, 0);
+}
+
+/**
+ * path_lookup_create - lookup a file path with open + create intent
+ * @name: pointer to file name
+ * @lookup_flags: lookup intent flags
+ * @nd: pointer to nameidata
+ * @open_flags: open intent flags
+ * @create_mode: create intent flags
+ */
+int path_lookup_create(const char *name, unsigned int lookup_flags,
+ struct nameidata *nd, int open_flags, int create_mode)
+{
+ return __path_lookup_intent_open(name, lookup_flags|LOOKUP_CREATE, nd,
+ open_flags, create_mode);
+}
+
+int __user_path_lookup_open(const char __user *name, unsigned int lookup_flags,
+ struct nameidata *nd, int open_flags)
+{
+ char *tmp = getname(name);
+ int err = PTR_ERR(tmp);
+
+ if (!IS_ERR(tmp)) {
+ err = __path_lookup_intent_open(tmp, lookup_flags, nd, open_flags, 0);
+ putname(tmp);
+ }
+ return err;
+}
+
/*
* Restricted form of lookup. Doesn't follow links, single-component only,
* needs parent already locked. Doesn't follow mounts.
@@ -1416,27 +1493,27 @@ int may_open(struct nameidata *nd, int a
*/
int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
{
- int acc_mode, error = 0;
+ int acc_mode, error;
struct path path;
struct dentry *dir;
int count = 0;

acc_mode = ACC_MODE(flag);

+ /* O_TRUNC implies we need access checks for write permissions */
+ if (flag & O_TRUNC)
+ acc_mode |= MAY_WRITE;
+
/* Allow the LSM permission hook to distinguish append
access from general write access. */
if (flag & O_APPEND)
acc_mode |= MAY_APPEND;

- /* Fill in the open() intent data */
- nd->intent.open.flags = flag;
- nd->intent.open.create_mode = mode;
-
/*
* The simplest case - just a plain lookup.
*/
if (!(flag & O_CREAT)) {
- error = path_lookup(pathname, lookup_flags(flag)|LOOKUP_OPEN, nd);
+ error = path_lookup_open(pathname, lookup_flags(flag), nd, flag);
if (error)
return error;
goto ok;
@@ -1445,7 +1522,7 @@ int open_namei(const char * pathname, in
/*
* Create - we need to know the parent.
*/
- error = path_lookup(pathname, LOOKUP_PARENT|LOOKUP_OPEN|LOOKUP_CREATE, nd);
+ error = path_lookup_create(pathname, LOOKUP_PARENT, nd, flag, mode);
if (error)
return error;

@@ -1520,6 +1597,8 @@ ok:
exit_dput:
dput_path(&path, nd);
exit:
+ if (!IS_ERR(nd->intent.open.file))
+ release_open_intent(nd);
path_release(nd);
return error;

Index: linux-2.6.14-rc4/fs/exec.c
===================================================================
--- linux-2.6.14-rc4.orig/fs/exec.c
+++ linux-2.6.14-rc4/fs/exec.c
@@ -126,8 +126,7 @@ asmlinkage long sys_uselib(const char __
struct nameidata nd;
int error;

- nd.intent.open.flags = FMODE_READ;
- error = __user_walk(library, LOOKUP_FOLLOW|LOOKUP_OPEN, &nd);
+ error = __user_path_lookup_open(library, LOOKUP_FOLLOW, &nd, FMODE_READ);
if (error)
goto out;

@@ -139,7 +138,7 @@ asmlinkage long sys_uselib(const char __
if (error)
goto exit;

- file = dentry_open(nd.dentry, nd.mnt, O_RDONLY);
+ file = nameidata_to_filp(&nd, O_RDONLY);
error = PTR_ERR(file);
if (IS_ERR(file))
goto out;
@@ -167,6 +166,7 @@ asmlinkage long sys_uselib(const char __
out:
return error;
exit:
+ release_open_intent(&nd);
path_release(&nd);
goto out;
}
@@ -490,8 +490,7 @@ struct file *open_exec(const char *name)
int err;
struct file *file;

- nd.intent.open.flags = FMODE_READ;
- err = path_lookup(name, LOOKUP_FOLLOW|LOOKUP_OPEN, &nd);
+ err = path_lookup_open(name, LOOKUP_FOLLOW, &nd, FMODE_READ);
file = ERR_PTR(err);

if (!err) {
@@ -504,7 +503,7 @@ struct file *open_exec(const char *name)
err = -EACCES;
file = ERR_PTR(err);
if (!err) {
- file = dentry_open(nd.dentry, nd.mnt, O_RDONLY);
+ file = nameidata_to_filp(&nd, O_RDONLY);
if (!IS_ERR(file)) {
err = deny_write_access(file);
if (err) {
@@ -516,6 +515,7 @@ out:
return file;
}
}
+ release_open_intent(&nd);
path_release(&nd);
}
goto out;
Index: linux-2.6.14-rc4/include/linux/namei.h
===================================================================
--- linux-2.6.14-rc4.orig/include/linux/namei.h
+++ linux-2.6.14-rc4/include/linux/namei.h
@@ -8,6 +8,7 @@ struct vfsmount;
struct open_intent {
int flags;
int create_mode;
+ struct file *file;
};

enum { MAX_NESTED_LINKS = 5 };
@@ -65,6 +66,13 @@ extern int FASTCALL(link_path_walk(const
extern void path_release(struct nameidata *);
extern void path_release_on_umount(struct nameidata *);

+extern int __user_path_lookup_open(const char __user *, unsigned lookup_flags, struct nameidata *nd, int open_flags);
+extern int path_lookup_open(const char *, unsigned lookup_flags, struct nameidata *, int open_flags);
+extern struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
+ int (*open)(struct inode *, struct file *));
+extern struct file *nameidata_to_filp(struct nameidata *nd, int flags);
+extern void release_open_intent(struct nameidata *);
+
extern struct dentry * lookup_one_len(const char *, struct dentry *, int);
extern struct dentry * lookup_hash(struct qstr *, struct dentry *);

Index: linux-2.6.14-rc4/fs/open.c
===================================================================
--- linux-2.6.14-rc4.orig/fs/open.c
+++ linux-2.6.14-rc4/fs/open.c
@@ -739,7 +739,8 @@ asmlinkage long sys_fchown(unsigned int
}

static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
- int flags, struct file *f)
+ int flags, struct file *f,
+ int (*open)(struct inode *, struct file *))
{
struct inode *inode;
int error;
@@ -761,11 +762,14 @@ static struct file *__dentry_open(struct
f->f_op = fops_get(inode->i_fop);
file_move(f, &inode->i_sb->s_files);

- if (f->f_op && f->f_op->open) {
- error = f->f_op->open(inode,f);
+ if (!open && f->f_op)
+ open = f->f_op->open;
+ if (open) {
+ error = open(inode, f);
if (error)
goto cleanup_all;
}
+
f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
@@ -814,28 +818,75 @@ struct file *filp_open(const char * file
{
int namei_flags, error;
struct nameidata nd;
- struct file *f;

namei_flags = flags;
if ((namei_flags+1) & O_ACCMODE)
namei_flags++;
- if (namei_flags & O_TRUNC)
- namei_flags |= 2;
-
- error = -ENFILE;
- f = get_empty_filp();
- if (f == NULL)
- return ERR_PTR(error);

error = open_namei(filename, namei_flags, mode, &nd);
if (!error)
- return __dentry_open(nd.dentry, nd.mnt, flags, f);
+ return nameidata_to_filp(&nd, flags);

- put_filp(f);
return ERR_PTR(error);
}
EXPORT_SYMBOL(filp_open);

+/**
+ * lookup_instantiate_filp - instantiates the open intent filp
+ * @nd: pointer to nameidata
+ * @dentry: pointer to dentry
+ * @open: open callback
+ *
+ * Helper for filesystems that want to use lookup open intents and pass back
+ * a fully instantiated struct file to the caller.
+ * This function is meant to be called from within a filesystem's
+ * lookup method.
+ * Note that in case of error, nd->intent.open.file is destroyed, but the
+ * path information remains valid.
+ * If the open callback is set to NULL, then the standard f_op->open()
+ * filesystem callback is substituted.
+ */
+struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
+ int (*open)(struct inode *, struct file *))
+{
+ if (IS_ERR(nd->intent.open.file))
+ goto out;
+ if (IS_ERR(dentry))
+ goto out_err;
+ nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->mnt),
+ nd->intent.open.flags - 1,
+ nd->intent.open.file,
+ open);
+out:
+ return nd->intent.open.file;
+out_err:
+ release_open_intent(nd);
+ nd->intent.open.file = (struct file *)dentry;
+ goto out;
+}
+EXPORT_SYMBOL_GPL(lookup_instantiate_filp);
+
+/**
+ * nameidata_to_filp - convert a nameidata to an open filp.
+ * @nd: pointer to nameidata
+ * @flags: open flags
+ *
+ * Note that this function destroys the original nameidata
+ */
+struct file *nameidata_to_filp(struct nameidata *nd, int flags)
+{
+ struct file *filp;
+
+ /* Pick up the filp from the open intent */
+ filp = nd->intent.open.file;
+ /* Has the filesystem initialised the file for us? */
+ if (filp->f_dentry == NULL)
+ filp = __dentry_open(nd->dentry, nd->mnt, flags, filp, NULL);
+ else
+ path_release(nd);
+ return filp;
+}
+
struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
{
int error;
@@ -846,7 +897,7 @@ struct file *dentry_open(struct dentry *
if (f == NULL)
return ERR_PTR(error);

- return __dentry_open(dentry, mnt, flags, f);
+ return __dentry_open(dentry, mnt, flags, f, NULL);
}
EXPORT_SYMBOL(dentry_open);
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