On Wed, 17 Aug 2011, Barry Song wrote: > From: Peiyu Li <peiyu.li@xxxxxxx> > > Now the mass storage driver has fixed logic block size of 512 bytes. > > The mass storage gadget read/write bound devices only through VFS, so the bottom level > devices actually are just RAW devices to the driver and connected PC. As a RAW, hosts > can always format, read and write it right in 512 bytes logic block and don't care about > the actual logic block size of devices bound to the gadget. > > But if we want to share the bound block device partition between target board and PC, > in case the logic block size of the bound block device is 4KB, we execute the following > steps: > 1. connect a board with mass storage gadget to PC(the board has set one partition of > on-board block device as file name of the mass storage) > 2. PC format the mass storage to VFAT by default logic block size and read/write it > 3. disconnect boards from PC > 4. target board mount the partition as VFAT > Step 4 will fail since kernel on target thinks the logic block size of the bound partition > as 4KB. > A typical error is > "FAT: logical sector size too small for device (logical sector size = 512)" > > If we execute opposite steps: > 1. format the partition to VFAT on target board and read/write this partition > 2. connect the board to Windows PC as usb mass storage gadget, windows will think the disk > is not formatted > > So the conclusion is that only as a gadget, the mass storage driver has no any problem. > But being shared VFAT or other filesystem on PC and target board, it will fail. > > This patch adapts logic block size to bound block devices and fix the issue. > > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Peiyu Li <peiyu.li@xxxxxxx> > Signed-off-by: Xianglong Du <xianglong.du@xxxxxxx> > Signed-off-by: Huayi Li <huayi.li@xxxxxxx> > Signed-off-by: Barry Song <Baohua.Song@xxxxxxx> > --- > -v2: > 1. While backing file is not block device, use fixed logic block size 512 > 2. for cdrom, use fixed logic block size 2048 > 3. change file_storage as well There's still one problem. The existing code assumes the block size is divisible by the bulk maxpacket size. If the block size were 256 or smaller, this would no longer be true. (In fact, we already have this problem now when people try to use g_file_storage or g_mass_storage running at SuperSpeed, because then the maxpacket size is 1024.) The only way to fix this is to remove the code that aligns the file transfers with the page size of the page cache. Would you like to write a preliminary patch to do that? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
