Read-only bind mounts (-mm resend)
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- v1 Latest27 patches 11 repliesIn review
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Reviews trailers per patch
16 of 27 patches have a Reviewed-by or Acked-by.
| Patch | Christoph Hellwig | Serge Hallyn |
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Trailers given in replies are filled; those carried in the patches from earlier versions are outlined with dashes.
Cover letter [PATCH 00/27] Read-only bind mounts (-mm resend)
This is against 2.6.24-rc1 + recent git.
I've integrated all of the fixes from mm, and included cleanups in a different order. This also includes some extra fput-time checking to ensure that we have balanced mount writer counts.
These replace the patches in -mm mostly because the new fixes require some cleanups that are functionally independent from the r/o bind mount code itself. These fixes precent the rest of the set and require some by hand merging.
If you're going to review one and only one patch, 17/27 (the one for "opend" files) is the most critical.
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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 are 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 this script:
http://sr71.net/~dave/linux/robind-test.sh
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.