-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Ram wrote: > On Wed, 2005-02-02 at 11:45, Mike Waychison wrote: > > 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. >
Well, fwiw, I have the same kind of race in autofsng. I counter it by building up the vfsmount tree elsewhere and mount --move'ing it. Unfortunately, the RFC states that moving a shared vfsmount is prohibited (for which the reasoning slips my mind). - -- 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 iD8DBQFCAUFQdQs4kOxk3/MRAksjAJ4wCzY7jc8aUGKeiHKTywFKxhN1qACeI4HM eO3XGtYgnbOZJYT3K1nbKd4= =wwuF -----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/
