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>
shmem_{nopage,mmap} are no longer used in ipc/shm.c
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The attached patch makes the SYSV IPC shared memory facilities use the new
ramfs facilities on a no-MMU kernel.
The following changes are made:
(1) There are now shmem_mmap() and shmem_get_unmapped_area() functions to
allow the IPC SHM facilities to commune with the tiny-shmem and shmem
code.
(2) ramfs files now need resizing using do_truncate() rather than by modifying
the inode size directly (see shmem_file_setup()). This causes ramfs to
attempt to bind a block of pages of sufficient size to the inode.
(3) CONFIG_SYSVIPC is no longer contingent on CONFIG_MMU.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
