Hi, ext3 has a problem that mmap writes end up allocating blocks only in writepage() callback. This then effectively invalidates any quota checking because writepage() is called from flusher thread thus with root priviledges. So any user is able to arbitrarily exceed quota limit using mmap write. The following four patches try to address this problem. The patches implement page_mkwrite() callback which allocates all necessary metadata and reserves space for data block (this is the main difference from the patches I was sending last autumn which did not allocate metadata). Then during writepage() (or write()) time the reservation gets converted into real block allocation. With this implementation I don't see any performance difference in heavy BerkleyDB load from the ext3 without these patches. Simple allocation in page_mkwrite() ends up being about 3x slower than this reservation scheme because of fragmentation. I've tested the patch on both x86_64 (1K and 4K blocksize) and ppc with 64k pages (1K and 4K blocksize) to catch possible bugs. I've also run tests in ENOSPC conditions and conditions when quota is getting exceeded. All these tests run fine with this version of patches (actually, I've triggered two genuine ext3 bugs during this testing which I'm going to merge separately). So I'd like to merge these patches but before I do that I'd like another pair of eyes to have a look at these changes... So comments are welcome. Maybe one more addition: As we spoke at LSF, we plan to remove ext3 driver from kernel. But it's still going to take significant amount of time (more than an year) so I'd like to have this serious issue fixed in ext3. Honza -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
