On Wed, 13 Jun 2012, Ted Ts'o wrote: > On Wed, Jun 13, 2012 at 08:43:47PM +0000, Arnd Bergmann wrote: > > > For SD cards, almost everyone is lying and we cannot trust the > > information, and for USB flash, there is no way to ask the device. > > In both of these cases, we probably want to detect the erase block > > size at mkfs time using some timing attack that I worked on before. > > Note that those devices also do not offer support for context IDs. > > Yes, although presumably aligning large files to erase block > boundaries would still be useful, yes? > > So adding an erase block size to the ext2/3/4 superblock sounds like a > first great step. By making it be a superblock field, that way it's > possible to override the value returned by the hardware if it turns > out to be a lie, and we can also use programs like flashbench to > figure out the erase block size and populate the superblock value via > some userspace process. (Possibly called out of mke2fs directly if we > can automate it completely, and make it dead reliable.) Let's not forget that, in almost all cases, filesystem images are not created live on the final medium. Factories are picking a batch of flash devices and a pre-built filesystem image is stamped on them, and there might not even be a guarantee that those flash devices will all have the same characteristics. So to say that making this tuning at mkfs time is probably not the best strategy. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
