path: root/ipc
diff options
authorDave Hansen <haveblue@us.ibm.com>2007-10-16 23:31:13 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-17 08:43:04 -0700
commitce8d2cdf3d2b73e346c82e6f0a46da331df6364c (patch)
treebf3597f2d4f57d6e30a7703d7fce0dbf8c757962 /ipc
parent348366b963e4e1462c8354827a9cb910aa865bf2 (diff)
r/o bind mounts: filesystem helpers for custom 'struct file's
Why do we need r/o bind mounts? This feature allows a read-only view into a read-write filesystem. In the process of doing that, it also provides infrastructure for keeping track of the number of writers to any given mount. This has a number of uses. It allows chroots to have parts of filesystems writable. It will be useful for containers in the future because users may have root inside a container, but should not be allowed to write to somefilesystems. This also replaces patches that vserver has had out of the tree for several years. It allows security enhancement by making sure that parts of your filesystem read-only (such as when you don't trust your FTP server), when you don't want to have entire new filesystems mounted, or when you want atime selectively updated. I've been using the following script to test that the feature is working as desired. It takes a directory and makes a regular bind and a r/o bind mount of it. It then performs some normal filesystem operations on the three directories, including ones that are expected to fail, like creating a file on the r/o mount. This patch: Some filesystems forego the vfs and may_open() and create their own 'struct file's. This patch creates a couple of helper functions which can be used by these filesystems, and will provide a unified place which the r/o bind mount code may patch. Also, rename an existing, static-scope init_file() to a less generic name. Signed-off-by: Dave Hansen <haveblue@us.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
1 files changed, 5 insertions, 8 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index b8884c288ecc..5fc5cf50cf1b 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -907,7 +907,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
goto out_unlock;
path.dentry = dget(shp->shm_file->f_path.dentry);
- path.mnt = mntget(shp->shm_file->f_path.mnt);
+ path.mnt = shp->shm_file->f_path.mnt;
size = i_size_read(path.dentry->d_inode);
@@ -915,18 +915,16 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
err = -ENOMEM;
sfd = kzalloc(sizeof(*sfd), GFP_KERNEL);
if (!sfd)
- goto out_put_path;
+ goto out_put_dentry;
err = -ENOMEM;
- file = get_empty_filp();
+ file = alloc_file(path.mnt, path.dentry, f_mode, &shm_file_operations);
if (!file)
goto out_free;
- file->f_op = &shm_file_operations;
file->private_data = sfd;
- file->f_path = path;
file->f_mapping = shp->shm_file->f_mapping;
- file->f_mode = f_mode;
sfd->id = shp->id;
sfd->ns = get_ipc_ns(ns);
sfd->file = shp->shm_file;
@@ -977,9 +975,8 @@ out_unlock:
- mntput(path.mnt);
goto out_nattch;

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