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>

3 files changed, 157 insertions, 27 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a04a575ad43..d2208f7c87d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -126,8 +126,7 @@ asmlinkage long sys_uselib(const char __user * library)
         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 __user * library)
         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 __user * library)
 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;
diff --git a/fs/namei.c b/fs/namei.c
index aa62dbda93a..0d1dff7d3d9 100644
--- a/fs/namei.c
+++ b/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 nameidata *nd)
         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 acc_mode, int flag)
  */
 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, int flag, int mode, struct nameidata *nd)
         /*
          * 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;
 
diff --git a/fs/open.c b/fs/open.c
index f0d90cf0495..8d06ec911fd 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -739,7 +739,8 @@ asmlinkage long sys_fchown(unsigned int fd, uid_t user, gid_t group)
 }
 
 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 dentry *dentry, struct vfsmount *mnt,
         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 * filename, int flags, int mode)
 {
         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 *dentry, struct vfsmount *mnt, int flags)
         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);