On Wed, 2005-02-02 at 11:45, Mike Waychison wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Ram wrote: > > On Tue, 2005-02-01 at 15:21, J. Bruce Fields wrote: > > > >>On Tue, Jan 25, 2005 at 01:07:12PM -0800, Ram wrote: > >> > >>>If there exists a private subtree in a larger shared subtree, what > >>>happens when the larger shared subtree is rbound to some other place? > >>>Is a new private subtree created in the new larger shared subtree? or > >>>will that be pruned out in the new larger subtree? > >> > >>"mount --rbind" will always do at least all the mounts that it did > >>before the introduction of shared subtrees--so certainly it will copy > >>private subtrees along with shared ones. (Since subtrees are private by > >>default, anything else would make --rbind do nothing by default.) My > >>understanding of Viro's RFC is that the new subtree will have no > >>connection with the preexisting private subtree (we want private > >>subtrees to stay private), but that the new copy will end up with > >>whatever propagation the target of the "mount --rbind" had. (So the > >>addition of the copy of the private subtree to the target vfsmount will > >>be replicated on any vfsmount that the target vfsmount propogates to, > >>and those copies will propagate among themselves in the same way that > >>the copies of the target vfsmount propagate to each other.) > > > > > > ok. that makes sense. As you said the private subtree shall get copied > > to the new location, however propogations wont be set in either > > directions. However I have a rather unusual requirement which forces > > multiple rbind of a shared subtree within the same shared subtree. > > > > I did the calculation and found that the tree simply explodes with > > vfsstructs. If I mark a subtree within the larger shared tree as > > private, then the number of vfsstructs grows linearly O(n). However if > > there was a way of marking a subtree within the larger shared tree as > > unclonable than the increase in number of vfsstruct is constant. > > > > What I am essentially driving at is, can we add another feature which > > allows me to mark a subtree as unclonable? > > > > > > Read below to see how the tree explodes: > > > > to run you through an example: > > > > (In case the tree pictures below gets garbled, it can also be seen at > > http://www.sudhaa.com/~ram/readahead/sharedsubtree/subtree ) > > > > step 1: > > lets say the root tree has just two directories with one vfsstruct. > > root > > / \ > > tmp usr > > All I want is to be able to see the entire root tree > > (but not anything under /root/tmp) to be viewable under /root/tmp/m* > > > > step2: > > mount --make-shared /root > > > > mkdir -p /tmp/m1 > > > > mount --rbind /root /tmp/m1 > > > > the new tree now looks like this: > > > > root > > / \ > > tmp usr > > / > > m1 > > / \ > > tmp usr > > / > > m1 > > > > it has two vfsstructs > > > > step3: > > mkdir -p /tmp/m2 > > mount --rbind /root /tmp/m2 > > At this step, you probably shouldn't be using --rbind, but --bind > instead to only bind a copy of the root vfsmount, so it now looks like: > > > root > > / \ > > tmp usr > > / \ > > m1 m2 > > / \ / \ > > tmp usr tmp usr > > / \ / \ > > m1 m2 m1 m2
Well I thought about this. Even Bruce Fields suggested this in a private thread. But this solution can be racy. You may have to do multiple binds for all the vfstructs that reside in the subtree under / (but not under /root/tmp). And doing it atomically without racing with other simultaneous mounts would be tricky. RP > > - -- > Mike Waychison > Sun Microsystems, Inc. > 1 (650) 352-5299 voice > 1 (416) 202-8336 voice > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > NOTICE: The opinions expressed in this email are held by me, > and may not represent the views of Sun Microsystems, Inc. > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.2.5 (GNU/Linux) > Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org > > iD8DBQFCAS3ndQs4kOxk3/MRAm/qAJ0awCE49/g+HhMdX0MBZnFLSp2IjACgj5EQ > El+YLq25hQeDAt9Y92nqoAU= > =so+d > -----END PGP SIGNATURE----- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
