On Wed, Jul 06, 2005 at 09:33:13PM -0500, David Masover wrote: > And speaking of which, the only doomsday scenario (running out of RAM) > that I can think of with this scheme is if we have a ton of hardlinks to > the same file and we try to move one of them. But this scales linearly > with the number of hardlinks, I think. Maybe not quite, but certainly > not exponentially. > > The only other doomsday scenario is if we have a ludicrously deep tree.
rename(a/b, c/b), if a and c are identical. End result, either you deadlock trying to lock the same object twice, or you end up removing b since the target of a rename is unlinked. The VFS uses dentries, there is one per hardlinked object, and they have a single parent only. So a/b and c/b are represented by the same inode, but they have completely different dentry-aliases associated with them. Similar things for removal, we can safely remove a file, but not a directory that still has children, if you have 'meta-files' hanging of a file, you'd have to get rid of the metadata objects first. If you want to use a file as a directory, it probably will need the same restrictions as a directory if you expect the dcache and VFS locking to work correctly. So that means, _no hardlinks to files_ (the file system could internally implement copy-on-write type links, or use a content addressable storage to deal with diskspace issues) and the file system probably has to d_unhash/destroy metadata objects before it can unlink the file object, etc. > To make this work in real usage, not DOS testing, we really need both of > those, and even then I'm not sure it can work. What's the maximum > number of hardlinks supported to a single file? I believe nlink is a 16-bit value, so that would be either 32K or 64K depending on signedness. > What's the maximum tree depth? Last time I checked, PATH_MAX is 4096, so that would be about 2048 single character directory names. > Can these be limited to prevent actual DOS attempts? Is that the 'nobody needs more than 64KB of memory' kind of DOS? Jan - 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/
