Commit efc6de0d authored by Peter Lieven's avatar Peter Lieven Committed by Paolo Bonzini
Browse files

block/iscsi: handle BUSY condition 



this patch adds handling of BUSY status reponse from an iSCSI target.
Currently, we fail with -EIO in case of SCSI_STATUS_BUSY while the
obvious reaction would be to retry the operation after some time.
The retry time is randomly choosen from a range with exponential
growth increasing with each retry.

This patch includes most of the changes by a an upcoming patch
from Stefan Hajnoczi:

 iscsi: implement .bdrv_detach/attach_aio_context()

because I also need the reference to the aio_context for
the retry timer to work. I included the changes to maintain
better mergeability.

Signed-off-by: default avatarPeter Lieven <pl@kamp.de>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent af44da87

block/iscsi.c

+43 −12
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#include "config-host.h"



#include <poll.h>

#include <math.h>

#include <arpa/inet.h>

#include "qemu-common.h"

#include "qemu/config-file.h"
@@ -75,6 +76,7 @@ typedef struct IscsiTask { 
    Coroutine *co;

    QEMUBH *bh;

    IscsiLun *iscsilun;

    QEMUTimer retry_timer;

} IscsiTask;



typedef struct IscsiAIOCB {
@@ -86,7 +88,6 @@ typedef struct IscsiAIOCB { 
    uint8_t *buf;

    int status;

    int canceled;

    int retries;

    int64_t sector_num;

    int nb_sectors;

#ifdef __linux__
@@ -96,7 +97,8 @@ typedef struct IscsiAIOCB { 


#define NOP_INTERVAL 5000

#define MAX_NOP_FAILURES 3

#define ISCSI_CMD_RETRIES 5

#define ISCSI_CMD_RETRIES ARRAY_SIZE(iscsi_retry_times)

static const unsigned iscsi_retry_times[] = {8, 32, 128, 512, 2048};



/* this threshhold is a trade-off knob to choose between

 * the potential additional overhead of an extra GET_LBA_STATUS request
@@ -146,6 +148,19 @@ static void iscsi_co_generic_bh_cb(void *opaque) 
    qemu_coroutine_enter(iTask->co, NULL);

}



static void iscsi_retry_timer_expired(void *opaque)

{

    struct IscsiTask *iTask = opaque;

    if (iTask->co) {

        qemu_coroutine_enter(iTask->co, NULL);

    }

}



static inline unsigned exp_random(double mean)

{

    return -mean * log((double)rand() / RAND_MAX);

}



static void

iscsi_co_generic_cb(struct iscsi_context *iscsi, int status,

                        void *command_data, void *opaque)
@@ -158,14 +173,30 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int status, 
    iTask->do_retry = 0;

    iTask->task = task;



    if (iTask->retries-- > 0 && status == SCSI_STATUS_CHECK_CONDITION

    if (status != SCSI_STATUS_GOOD) {

        if (iTask->retries++ < ISCSI_CMD_RETRIES) {

            if (status == SCSI_STATUS_CHECK_CONDITION

                && task->sense.key == SCSI_SENSE_UNIT_ATTENTION) {

        error_report("iSCSI CheckCondition: %s", iscsi_get_error(iscsi));

                error_report("iSCSI CheckCondition: %s",

                             iscsi_get_error(iscsi));

                iTask->do_retry = 1;

                goto out;

            }



    if (status != SCSI_STATUS_GOOD) {

            if (status == SCSI_STATUS_BUSY) {

                unsigned retry_time =

                    exp_random(iscsi_retry_times[iTask->retries - 1]);

                error_report("iSCSI Busy (retry #%u in %u ms): %s",

                             iTask->retries, retry_time,

                             iscsi_get_error(iscsi));

                aio_timer_init(iTask->iscsilun->aio_context,

                               &iTask->retry_timer, QEMU_CLOCK_REALTIME,

                               SCALE_MS, iscsi_retry_timer_expired, iTask);

                timer_mod(&iTask->retry_timer,

                          qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + retry_time);

                iTask->do_retry = 1;

                return;

            }

        }

        error_report("iSCSI Failure: %s", iscsi_get_error(iscsi));

    }