* May be copied or modified under the terms of the GNU General Public
* License. See linux/COPYING for more information.
*
- * Packet writing layer for ATAPI and SCSI CD-R, CD-RW, DVD-R, and
- * DVD-RW devices (aka an exercise in block layer masturbation)
+ * Packet writing layer for ATAPI and SCSI CD-RW, DVD+RW, DVD-RW and
+ * DVD-RAM devices.
*
+ * Theory of operation:
*
- * TODO: (circa order of when I will fix it)
- * - Only able to write on CD-RW media right now.
- * - check host application code on media and set it in write page
- * - interface for UDF <-> packet to negotiate a new location when a write
- * fails.
- * - handle OPC, especially for -RW media
+ * At the lowest level, there is the standard driver for the CD/DVD device,
+ * typically ide-cd.c or sr.c. This driver can handle read and write requests,
+ * but it doesn't know anything about the special restrictions that apply to
+ * packet writing. One restriction is that write requests must be aligned to
+ * packet boundaries on the physical media, and the size of a write request
+ * must be equal to the packet size. Another restriction is that a
+ * GPCMD_FLUSH_CACHE command has to be issued to the drive before a read
+ * command, if the previous command was a write.
*
- * Theory of operation:
+ * The purpose of the packet writing driver is to hide these restrictions from
+ * higher layers, such as file systems, and present a block device that can be
+ * randomly read and written using 2kB-sized blocks.
*
- * We use a custom make_request_fn function that forwards reads directly to
- * the underlying CD device. Write requests are either attached directly to
- * a live packet_data object, or simply stored sequentially in a list for
- * later processing by the kcdrwd kernel thread. This driver doesn't use
- * any elevator functionally as defined by the elevator_s struct, but the
- * underlying CD device uses a standard elevator.
+ * The lowest layer in the packet writing driver is the packet I/O scheduler.
+ * Its data is defined by the struct packet_iosched and includes two bio
+ * queues with pending read and write requests. These queues are processed
+ * by the pkt_iosched_process_queue() function. The write requests in this
+ * queue are already properly aligned and sized. This layer is responsible for
+ * issuing the flush cache commands and scheduling the I/O in a good order.
*
- * This strategy makes it possible to do very late merging of IO requests.
- * A new bio sent to pkt_make_request can be merged with a live packet_data
- * object even if the object is in the data gathering state.
+ * The next layer transforms unaligned write requests to aligned writes. This
+ * transformation requires reading missing pieces of data from the underlying
+ * block device, assembling the pieces to full packets and queuing them to the
+ * packet I/O scheduler.
+ *
+ * At the top layer there is a custom make_request_fn function that forwards
+ * read requests directly to the iosched queue and puts write requests in the
+ * unaligned write queue. A kernel thread performs the necessary read
+ * gathering to convert the unaligned writes to aligned writes and then feeds
+ * them to the packet I/O scheduler.
*
*************************************************************************/
* Queue a bio for processing by the low-level CD device. Must be called
* from process context.
*/
-static void pkt_queue_bio(struct pktcdvd_device *pd, struct bio *bio, int high_prio_read)
+static void pkt_queue_bio(struct pktcdvd_device *pd, struct bio *bio)
{
spin_lock(&pd->iosched.lock);
if (bio_data_dir(bio) == READ) {
pkt_add_list_last(bio, &pd->iosched.read_queue,
&pd->iosched.read_queue_tail);
- if (high_prio_read)
- pd->iosched.high_prio_read = 1;
} else {
pkt_add_list_last(bio, &pd->iosched.write_queue,
&pd->iosched.write_queue_tail);
* requirements for CDRW drives:
* - A cache flush command must be inserted before a read request if the
* previous request was a write.
- * - Switching between reading and writing is slow, so don't it more often
+ * - Switching between reading and writing is slow, so don't do it more often
* than necessary.
+ * - Optimize for throughput at the expense of latency. This means that streaming
+ * writes will never be interrupted by a read, but if the drive has to seek
+ * before the next write, switch to reading instead if there are any pending
+ * read requests.
* - Set the read speed according to current usage pattern. When only reading
* from the device, it's best to use the highest possible read speed, but
* when switching often between reading and writing, it's better to have the
* same read and write speeds.
- * - Reads originating from user space should have higher priority than reads
- * originating from pkt_gather_data, because some process is usually waiting
- * on reads of the first kind.
*/
static void pkt_iosched_process_queue(struct pktcdvd_device *pd)
{
for (;;) {
struct bio *bio;
- int reads_queued, writes_queued, high_prio_read;
+ int reads_queued, writes_queued;
spin_lock(&pd->iosched.lock);
reads_queued = (pd->iosched.read_queue != NULL);
writes_queued = (pd->iosched.write_queue != NULL);
- if (!reads_queued)
- pd->iosched.high_prio_read = 0;
- high_prio_read = pd->iosched.high_prio_read;
spin_unlock(&pd->iosched.lock);
if (!reads_queued && !writes_queued)
break;
if (pd->iosched.writing) {
- if (high_prio_read || (!writes_queued && reads_queued)) {
+ int need_write_seek = 1;
+ spin_lock(&pd->iosched.lock);
+ bio = pd->iosched.write_queue;
+ spin_unlock(&pd->iosched.lock);
+ if (bio && (bio->bi_sector == pd->iosched.last_write))
+ need_write_seek = 0;
+ if (need_write_seek && reads_queued) {
if (atomic_read(&pd->cdrw.pending_bios) > 0) {
VPRINTK("pktcdvd: write, waiting\n");
break;
if (bio_data_dir(bio) == READ)
pd->iosched.successive_reads += bio->bi_size >> 10;
- else
+ else {
pd->iosched.successive_reads = 0;
+ pd->iosched.last_write = bio->bi_sector + bio_sectors(bio);
+ }
if (pd->iosched.successive_reads >= HI_SPEED_SWITCH) {
if (pd->read_speed == pd->write_speed) {
pd->read_speed = MAX_SPEED;
atomic_inc(&pkt->io_wait);
bio->bi_rw = READ;
- pkt_queue_bio(pd, bio, 0);
+ pkt_queue_bio(pd, bio);
frames_read++;
}
pd->current_sector = zone + pd->settings.size;
pkt->sector = zone;
pkt->frames = pd->settings.size >> 2;
- BUG_ON(pkt->frames > PACKET_MAX_SIZE);
pkt->write_size = 0;
/*
atomic_set(&pkt->io_wait, 1);
pkt->w_bio->bi_rw = WRITE;
- pkt_queue_bio(pd, pkt->w_bio, 0);
+ pkt_queue_bio(pd, pkt->w_bio);
}
static void pkt_finish_packet(struct packet_data *pkt, int uptodate)
VPRINTK("kcdrwd: wake up\n");
/* make swsusp happy with our thread */
- if (current->flags & PF_FREEZE)
- refrigerator(PF_FREEZE);
+ try_to_freeze();
list_for_each_entry(pkt, &pd->cdrw.pkt_active_list, list) {
if (!pkt->sleep_time)
printk("pktcdvd: detected zero packet size!\n");
pd->settings.size = 128;
}
+ if (pd->settings.size > PACKET_MAX_SECTORS) {
+ printk("pktcdvd: packet size is too big\n");
+ return -ENXIO;
+ }
pd->settings.fp = ti.fp;
pd->offset = (be32_to_cpu(ti.track_start) << 2) & (pd->settings.size - 1);
cloned_bio->bi_private = psd;
cloned_bio->bi_end_io = pkt_end_io_read_cloned;
pd->stats.secs_r += bio->bi_size >> 9;
- pkt_queue_bio(pd, cloned_bio, 1);
+ pkt_queue_bio(pd, cloned_bio);
return 0;
}
projects / powerpc.git / blobdiff