On Tue, Feb 12 2008 at 19:54 +0200, Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > On Tue, Feb 12 2008 at 19:48 +0200, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> On Sun, Feb 10, 2008 at 09:09:41PM +0200, Boaz Harrosh wrote: >>> - add varlen_cdb and varlen_cdb_len to hold a large user cdb >>> if needed. They start as empty. Allocation of buffer must >>> be done by user and held until request execution is done. >>> - Since there can be either a fix_length command up to 16 bytes >>> or a variable_length, larger then 16 bytes, commands but never >>> both, we hold the two types in a union to save space. The >>> presence of varlen_cdb_len and cmd_len==0 signals a varlen_cdb >>> mode. >> this one I'm a bit confused by, why can't we just set the length >> of the variable length command in cmd_len aswell, and if cmd_len > >> the length of the cmd array it's a variable length command? >> >> Note that this is both to keep the logic simpler and not to grow >> struct request further. Especially for the rather rare case >> of a bidi command. > > Because this will be dangerous for the Legacy block devices. > Unlike scsi drivers block drivers do not have a .max_cmnd_len > and upper layer will not check to make sure that the device supports > the longer command. If such a command goes through, lets say bsg > the drivers do blindly memcpy(,,rq->cmd_len) and will crash. > Better safe then sorry, at no cost. > > Boaz > > - PS: the struct request does not grow. Because before cmd_len was unsigned but now both cmd_len and varlen_cdb_len are short so it is the same as before. Boaz - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
