[PATCH -V7 4/9] vfs: Add open by file handle support

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 fs/namei.c            |   24 ---------
 fs/open.c             |  136 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/namei.h |   24 +++++++++
 3 files changed, 160 insertions(+), 24 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a7dce91..a18711e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1521,30 +1521,6 @@ out_unlock:
 	return may_open(&nd->path, 0, open_flag & ~O_TRUNC);
 }
 
-/*
- * Note that while the flag value (low two bits) for sys_open means:
- *	00 - read-only
- *	01 - write-only
- *	10 - read-write
- *	11 - special
- * it is changed into
- *	00 - no permissions needed
- *	01 - read-permission
- *	10 - write-permission
- *	11 - read-write
- * for the internal routines (ie open_namei()/follow_link() etc)
- * This is more logical, and also allows the 00 "no perm needed"
- * to be used for symlinks (where the permissions are checked
- * later).
- *
-*/
-static inline int open_to_namei_flags(int flag)
-{
-	if ((flag+1) & O_ACCMODE)
-		flag++;
-	return flag;
-}
-
 static int open_will_truncate(int flag, struct inode *inode)
 {
 	/*
diff --git a/fs/open.c b/fs/open.c
index 9a34b81..348a1b9 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1315,3 +1315,139 @@ err_out:
 	asmlinkage_protect(4, ret, dfd, name, handle, flag);
 	return ret;
 }
+
+static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
+{
+	return 1;
+}
+
+static struct dentry *handle_to_dentry(struct vfsmount *mnt,
+				struct file_handle *handle)
+{
+	int handle_size;
+	struct dentry *dentry;
+
+	/* change the handle size to multiple of sizeof(u32) */
+	handle_size = handle->handle_size >> 2;
+	dentry = exportfs_decode_fh(mnt, (struct fid *)handle->f_handle,
+					handle_size, handle->handle_type,
+					vfs_dentry_acceptable, NULL);
+	return dentry;
+}
+
+static long do_sys_open_by_handle(struct file_handle __user *ufh, int flags)
+{
+	int fd;
+	int retval = 0;
+	int d_flags  = flags;
+	struct file *filp;
+	struct vfsmount *mnt;
+	struct inode *inode;
+	struct dentry *dentry;
+	struct file_handle f_handle;
+	struct file_handle *handle = NULL;
+
+	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
+		retval = -EFAULT;
+		goto out_err;
+	}
+	if ((f_handle.handle_size > MAX_HANDLE_SZ) ||
+		(f_handle.handle_size <= 0)) {
+		retval =  -EINVAL;
+		goto out_err;
+	}
+	if (!capable(CAP_DAC_OVERRIDE)) {
+		retval = -EPERM;
+		goto out_err;
+	}
+	/*
+	 * Find the vfsmount for this uuid in the
+	 * current namespace
+	 */
+	mnt = fs_get_vfsmount(current, &f_handle.fsid);
+	if (!mnt) {
+		retval = -ESTALE;
+		goto out_err;
+	}
+
+	handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_size,
+			GFP_KERNEL);
+	if (!handle) {
+		retval =  -ENOMEM;
+		goto out_mnt;
+	}
+	/* copy the full handle */
+	if (copy_from_user(handle, ufh,
+				sizeof(struct file_handle) +
+				f_handle.handle_size)) {
+		retval = -EFAULT;
+		goto out_mnt;
+	}
+	dentry = handle_to_dentry(mnt, handle);
+	if (IS_ERR(dentry)) {
+		retval = PTR_ERR(dentry);
+		goto out_mnt;
+	}
+	inode = dentry->d_inode;
+	flags  = open_to_namei_flags(flags);
+	/* O_TRUNC implies we need access checks for write permissions */
+	if (flags & O_TRUNC)
+		flags |= MAY_WRITE;
+
+	if ((!(flags & O_APPEND) || (flags & O_TRUNC)) &&
+		(flags & FMODE_WRITE) && IS_APPEND(inode)) {
+		retval = -EPERM;
+		goto out_dentry;
+	}
+	if ((flags & FMODE_WRITE) && IS_IMMUTABLE(inode)) {
+		retval = -EACCES;
+		goto out_dentry;
+	}
+	/* Can't write directories. */
+	if (S_ISDIR(inode->i_mode) && (flags & FMODE_WRITE)) {
+		retval = -EISDIR;
+		goto out_dentry;
+	}
+	fd = get_unused_fd_flags(d_flags);
+	if (fd < 0) {
+		retval = fd;
+		goto out_dentry;
+	}
+	filp = dentry_open(dget(dentry), mntget(mnt),
+			d_flags, current_cred());
+	if (IS_ERR(filp)) {
+		put_unused_fd(fd);
+		retval =  PTR_ERR(filp);
+		goto out_dentry;
+	}
+	if (inode->i_mode & S_IFREG) {
+		filp->f_flags |= O_NOATIME;
+		filp->f_mode |= FMODE_NOCMTIME;
+	}
+	fsnotify_open(filp->f_path.dentry);
+	fd_install(fd, filp);
+	retval = fd;
+
+out_dentry:
+	dput(dentry);
+out_mnt:
+	kfree(handle);
+	mntput(mnt);
+out_err:
+	return retval;
+}
+
+SYSCALL_DEFINE2(open_by_handle, struct file_handle __user *, handle,
+		int, flags)
+{
+	long ret;
+
+	if (force_o_largefile())
+		flags |= O_LARGEFILE;
+
+	ret = do_sys_open_by_handle(handle, flags);
+
+	/* avoid REGPARM breakage on x86: */
+	asmlinkage_protect(2, ret, handle, flags);
+	return ret;
+}
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 05b441d..a853aa0 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -4,6 +4,7 @@
 #include <linux/dcache.h>
 #include <linux/linkage.h>
 #include <linux/path.h>
+#include <asm-generic/fcntl.h>
 
 struct vfsmount;
 
@@ -96,4 +97,27 @@ static inline void nd_terminate_link(void *name, size_t len, size_t maxlen)
 	((char *) name)[min(len, maxlen)] = '\0';
 }
 
+/*
+ * Note that while the flag value (low two bits) for sys_open means:
+ *	00 - read-only
+ *	01 - write-only
+ *	10 - read-write
+ *	11 - special
+ * it is changed into
+ *	00 - no permissions needed
+ *	01 - read-permission
+ *	10 - write-permission
+ *	11 - read-write
+ * for the internal routines (ie open_namei()/follow_link() etc)
+ * This is more logical, and also allows the 00 "no perm needed"
+ * to be used for symlinks (where the permissions are checked
+ * later).
+ *
+*/
+static inline int open_to_namei_flags(int flag)
+{
+	if ((flag+1) & O_ACCMODE)
+		flag++;
+	return flag;
+}
 #endif /* _LINUX_NAMEI_H */
-- 
1.7.1.78.g212f0