Messages in this thread |  | | | Date | Tue, 27 Jun 2006 18:38:22 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH 00/20] Mount writer count and read-only bind mounts (v3) |
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On Tue, 27 Jun 2006 15:14:36 -0700 Dave Hansen <haveblue@us.ibm.com> wrote:
> I think these are ready for -mm. They've gone through a few revisions > and a week or two of normal burn-in testing. > > --- > > The following series implements read-only 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. New in this version is that > if that number is non-zero, remounts from r/w to r/o are not allowed. > > This set does not take the previously tried approach of pushing down > the vfsmount structure deeply into call paths, such that it might be > checked in functions like permission(), may_create() and may_open(). > Instead, it does checks near the entry points in the kernel, bumping > a reference count in the vfsmount structure. I've also eliminated > the use of the MNT_RDONLY flag. It was redundant since we have the > reference count. > > This set also makes no attempt to keep the return codes for these > r/o bind mounts the same as for a real r/o filesystem or device. > It would require significantly more code and be quite a bit more > invasive. Unless there is a very strong reason to do so, I believe > it isn't worth the trouble. > > One note: the previous patches all worked this way: > > mount --bind -o ro /source /dest > > These patches have changed that behavior. It now requires two steps: > > mount --bind /source /dest > mount -o remount,ro /dest
That seems a step backwards.
> Since the last revision, the locking in faccessat() and > mnt_is_readonly() has been changed to fix a race which might have > caused a false-negative mount-is-readonly return when faccessat() > is called while another two processes are racing to make a mount > readonly. > > Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
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