path: root/drivers/usb/storage/transport.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Driver for USB Mass Storage compliant devices
 *
 * Current development and maintenance by:
 *   (c) 1999-2002 Matthew Dharm (mdharm-usb@one-eyed-alien.net)
 *
 * Developed with the assistance of:
 *   (c) 2000 David L. Brown, Jr. (usb-storage@davidb.org)
 *   (c) 2000 Stephen J. Gowdy (SGowdy@lbl.gov)
 *   (c) 2002 Alan Stern <stern@rowland.org>
 *
 * Initial work by:
 *   (c) 1999 Michael Gee (michael@linuxspecific.com)
 *
 * This driver is based on the 'USB Mass Storage Class' document. This
 * describes in detail the protocol used to communicate with such
 * devices.  Clearly, the designers had SCSI and ATAPI commands in
 * mind when they created this document.  The commands are all very
 * similar to commands in the SCSI-II and ATAPI specifications.
 *
 * It is important to note that in a number of cases this class
 * exhibits class-specific exemptions from the USB specification.
 * Notably the usage of NAK, STALL and ACK differs from the norm, in
 * that they are used to communicate wait, failed and OK on commands.
 *
 * Also, for certain devices, the interrupt endpoint is used to convey
 * status of a command.
 */

#include <linux/sched.h>
#include <linux/gfp.h>
#include <linux/errno.h>
#include <linux/export.h>

#include <linux/usb/quirks.h>

#include <scsi/scsi.h>
#include <scsi/scsi_eh.h>
#include <scsi/scsi_device.h>

#include "usb.h"
#include "transport.h"
#include "protocol.h"
#include "scsiglue.h"
#include "debug.h"

#include <linux/blkdev.h>
#include "../../scsi/sd.h"


/***********************************************************************
 * Data transfer routines
 ***********************************************************************/

/*
 * This is subtle, so pay attention:
 * ---------------------------------
 * We're very concerned about races with a command abort.  Hanging this code
 * is a sure fire way to hang the kernel.  (Note that this discussion applies
 * only to transactions resulting from a scsi queued-command, since only
 * these transactions are subject to a scsi abort.  Other transactions, such
 * as those occurring during device-specific initialization, must be handled
 * by a separate code path.)
 *
 * The abort function (usb_storage_command_abort() in scsiglue.c) first
 * sets the machine state and the ABORTING bit in us->dflags to prevent
 * new URBs from being submitted.  It then calls usb_stor_stop_transport()
 * below, which atomically tests-and-clears the URB_ACTIVE bit in us->dflags
 * to see if the current_urb needs to be stopped.  Likewise, the SG_ACTIVE
 * bit is tested to see if the current_sg scatter-gather request needs to be
 * stopped.  The timeout callback routine does much the same thing.
 *
 * When a disconnect occurs, the DISCONNECTING bit in us->dflags is set to
 * prevent new URBs from being submitted, and usb_stor_stop_transport() is
 * called to stop any ongoing requests.
 *
 * The submit function first verifies that the submitting is allowed
 * (neither ABORTING nor DISCONNECTING bits are set) and that the submit
 * completes without errors, and only then sets the URB_ACTIVE bit.  This
 * prevents the stop_transport() function from trying to cancel the URB
 * while the submit call is underway.  Next, the submit function must test
 * the flags to see if an abort or disc