[RFC][PATCH 22/27] sys_mknodat(): elevate write count for vfs_mknod/create()

[Dave Hansen <haveblue@us.ibm.com>]

This takes care of all of the direct callers of vfs_mknod().
Since a few of these cases also handle normal file creation
as well, this also covers some calls to vfs_create().

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 ipc/mqueue.c                |    0 
 lxc-dave/fs/namei.c         |   48 ++++++++++++++++++++++++++++----------------
 lxc-dave/fs/nfsd/vfs.c      |    4 +++
 lxc-dave/net/unix/af_unix.c |    4 +++
 4 files changed, 39 insertions(+), 17 deletions(-)

diff -puN fs/namei.c~elevate-writers-vfs_mknod-try2 fs/namei.c
--- lxc/fs/namei.c~elevate-writers-vfs_mknod-try2	2006-06-07 16:53:25.000000000 -0700
+++ lxc-dave/fs/namei.c	2006-06-07 16:53:25.000000000 -0700
@@ -1852,26 +1852,40 @@ asmlinkage long sys_mknodat(int dfd, con
 
 	if (!IS_POSIXACL(nd.dentry->d_inode))
 		mode &= ~current->fs->umask;
-	if (!IS_ERR(dentry)) {
-		switch (mode & S_IFMT) {
-		case 0: case S_IFREG:
-			error = vfs_create(nd.dentry->d_inode,dentry,mode,&nd);
-			break;
-		case S_IFCHR: case S_IFBLK:
-			error = vfs_mknod(nd.dentry->d_inode,dentry,mode,
-					new_decode_dev(dev));
-			break;
-		case S_IFIFO: case S_IFSOCK:
-			error = vfs_mknod(nd.dentry->d_inode,dentry,mode,0);
+	if (IS_ERR(dentry))
+		goto out_unlock;
+	error = mnt_want_write(nd.mnt);
+	if (error)
+		goto out_dput;
+	switch (mode & S_IFMT) {
+	case 0: case S_IFREG:
+		error = vfs_create(nd.dentry->d_inode,dentry,mode,&nd);
+		break;
+	case S_IFCHR: case S_IFBLK:
+		error = mnt_want_write(nd.mnt);
+		if (error)
 			break;
-		case S_IFDIR:
-			error = -EPERM;
+		error = vfs_mknod(nd.dentry->d_inode,dentry,mode,
+				new_decode_dev(dev));
+		mnt_drop_write(nd.mnt);
+		break;
+	case S_IFIFO: case S_IFSOCK:
+		error = mnt_want_write(nd.mnt);
+		if (error)
 			break;
-		default:
-			error = -EINVAL;
-		}
-		dput(dentry);
+		error = vfs_mknod(nd.dentry->d_inode,dentry,mode,0);
+		mnt_drop_write(nd.mnt);
+		break;
+	case S_IFDIR:
+		error = -EPERM;
+		break;
+	default:
+		error = -EINVAL;
 	}
+	mnt_drop_write(nd.mnt);
+out_dput:
+	dput(dentry);
+out_unlock:
 	mutex_unlock(&nd.dentry->d_inode->i_mutex);
 	path_release(&nd);
 out:
diff -puN fs/nfsd/vfs.c~elevate-writers-vfs_mknod-try2 fs/nfsd/vfs.c
--- lxc/fs/nfsd/vfs.c~elevate-writers-vfs_mknod-try2	2006-06-07 16:53:25.000000000 -0700
+++ lxc-dave/fs/nfsd/vfs.c	2006-06-07 16:53:25.000000000 -0700
@@ -1153,6 +1153,9 @@ nfsd_create(struct svc_rqst *rqstp, stru
 	/*
 	 * Get the dir op function pointer.
 	 */
+	err = mnt_want_write(fhp->fh_export->ex_mnt);
+	if (err)
+		goto out_nfserr;
 	err = nfserr_perm;
 	switch (type) {
 	case S_IFREG:
@@ -1171,6 +1174,7 @@ nfsd_create(struct svc_rqst *rqstp, stru
 	        printk("nfsd: bad file type %o in nfsd_create\n", type);
 		err = -EINVAL;
 	}
+	mnt_drop_write(fhp->fh_export->ex_mnt);
 	if (err < 0)
 		goto out_nfserr;
 
diff -puN net/unix/af_unix.c~elevate-writers-vfs_mknod-try2 net/unix/af_unix.c
--- lxc/net/unix/af_unix.c~elevate-writers-vfs_mknod-try2	2006-06-07 16:53:25.000000000 -0700
+++ lxc-dave/net/unix/af_unix.c	2006-06-07 16:53:25.000000000 -0700
@@ -789,7 +789,11 @@ static int unix_bind(struct socket *sock
 		 */
 		mode = S_IFSOCK |
 		       (SOCK_INODE(sock)->i_mode & ~current->fs->umask);
+		err = mnt_want_write(nd.mnt);
+		if (err)
+			goto out_mknod_dput;
 		err = vfs_mknod(nd.dentry->d_inode, dentry, mode, 0);
+		mnt_drop_write(nd.mnt);
 		if (err)
 			goto out_mknod_dput;
 		mutex_unlock(&nd.dentry->d_inode->i_mutex);
diff -puN ipc/mqueue.c~elevate-writers-vfs_mknod-try2 ipc/mqueue.c
diff -L xattr.patch -puN /dev/null /dev/null
_