On Tue, Mar 10, 2026 at 11:49:22AM +0000, John Garry wrote:
> Add basic support just to get the per-port group state.
>
> This support does not account of state transitioning, sdev port group
> reconfiguration, etc, required for full support.
>
> libmultipath callbacks scsi_mpath_is_optimized() and
> scsi_mpath_is_disabled() are updated to take account of the ALUA-provided
> path information.
>
> As before, for no ALUA support (and scsi_multipath_always on) we assume
> that the paths are all optimized.
>
> Much of this code in scsi_mpath_alua_init() is copied from scsi_dh_alua.c,
> originally authored by Hannes Reinecke.
>
> Signed-off-by: John Garry <[email protected]>
> ---
> drivers/scsi/scsi_multipath.c | 163 ++++++++++++++++++++++++++++++++--
> include/scsi/scsi_multipath.h | 3 +
> 2 files changed, 160 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
> index 1489c7e979167..0a314080bf0a5 100644
> --- a/drivers/scsi/scsi_multipath.c
> +++ b/drivers/scsi/scsi_multipath.c
> @@ -4,6 +4,7 @@
> *
> */
>
> +#include <scsi/scsi_alua.h>
> #include <scsi/scsi_cmnd.h>
> #include <scsi/scsi_driver.h>
> #include <scsi/scsi_proto.h>
> @@ -346,18 +347,29 @@ static bool scsi_mpath_is_disabled(struct mpath_device
> *mpath_device)
> to_scsi_mpath_device(mpath_device);
> struct scsi_device *sdev = scsi_mpath_dev->sdev;
> enum scsi_device_state sdev_state = sdev->sdev_state;
> + int alua_state = scsi_mpath_dev->alua_state;
>
> if (sdev_state == SDEV_RUNNING || sdev_state == SDEV_CANCEL)
> return false;
>
> - return true;
> + if (alua_state == SCSI_ACCESS_STATE_OPTIMAL ||
> + alua_state == SCSI_ACCESS_STATE_ACTIVE)
> + return true;
> +
> + return false;
> }
>
> static bool scsi_mpath_is_optimized(struct mpath_device *mpath_device)
> {
> + struct scsi_mpath_device *scsi_mpath_dev =
> + to_scsi_mpath_device(mpath_device);
> +
> if (scsi_mpath_is_disabled(mpath_device))
> return false;
> - return true;
> + if (scsi_mpath_dev->alua_state == SCSI_ACCESS_STATE_OPTIMAL)
> + return true;
> + return false;
> +
> }
>
> /* Until we have ALUA support, we're always optimised */
> @@ -366,7 +378,7 @@ static enum mpath_access_state
> scsi_mpath_get_access_state(
> {
> if (scsi_mpath_is_disabled(mpath_device))
> return MPATH_STATE_INVALID;
> - return MPATH_STATE_OPTIMIZED;
> + return scsi_mpath_is_optimized(mpath_device);
> }
>
> static bool scsi_mpath_available_path(struct mpath_device *mpath_device,
> bool *available)
> @@ -579,16 +591,147 @@ static void scsi_multipath_sdev_uninit(struct
> scsi_device *sdev)
> sdev->scsi_mpath_dev = NULL;
> }
>
> +static int scsi_mpath_alua_init(struct scsi_device *sdev)
> +{
> + struct scsi_mpath_device *scsi_mpath_dev = sdev->scsi_mpath_dev;
> + struct scsi_sense_hdr sense_hdr;
> + int len, k, off, bufflen = ALUA_RTPG_SIZE;
> + unsigned char *desc, *buff;
> + unsigned int tpg_desc_tbl_off;
> + int group_id, rel_port = -1;
> + bool ext_hdr_unsupp = false;
> + int ret;
> +
> + group_id = scsi_vpd_tpg_id(sdev, &rel_port);
> + if (group_id < 0) {
> + /*
> + * Internal error; TPGS supported but required
> + * VPD identification descriptors not present.
> + * Disable ALUA support.
> + */
> + sdev_printk(KERN_INFO, sdev,
> + "%s: No target port descriptors found\n",
> + __func__);
> + return -EIO;
> + }
> +
> + buff = kzalloc(bufflen, GFP_KERNEL);
> + if (!buff)
> + return -ENOMEM;
> + retry:
> + ret = submit_rtpg(sdev, buff, bufflen, &sense_hdr,
> + ext_hdr_unsupp);
> +
> + if (ret) {
> + if (ret < 0 || !scsi_sense_valid(&sense_hdr)) {
> + sdev_printk(KERN_INFO, sdev,
> + "%s: rtpg failed, result %d\n",
> + __func__, ret);
> + kfree(buff);
> + if (ret < 0)
> + return -EBUSY;
> + if (host_byte(ret) == DID_NO_CONNECT)
> + return -ENODEV;
> + return -EIO;
> + }
> +
> + /*
> + * submit_rtpg() has failed on existing arrays
> + * when requesting extended header info, and
> + * the array doesn't support extended headers,
> + * even though it shouldn't according to T10.
> + * The retry without rtpg_ext_hdr_req set
> + * handles this.
> + * Note: some arrays return a sense key of ILLEGAL_REQUEST
> + * with ASC 00h if they don't support the extended header.
> + */
> + if (ext_hdr_unsupp &&
> + sense_hdr.sense_key == ILLEGAL_REQUEST) {
> + ext_hdr_unsupp = true;
> + goto retry;
> + }
> + /*
> + * If the array returns with 'ALUA state transition'
> + * sense code here it cannot return RTPG data during
> + * transition. So set the state to 'transitioning' directly.
> + */
> + if (sense_hdr.sense_key == NOT_READY &&
> + sense_hdr.asc == 0x04 && sense_hdr.ascq == 0x0a)
> + goto out;
This check is odd. First, we don't set the state to 'transitioning' like
the comment says. We don't set alua_state at all, which ends up meaning
that it stays as 0 (SCSI_ACCESS_STATE_OPTIMAL). It seems like we should
explicitly set it and make the comment reflect that, if just to aid
understanding of the logic.
Nitpick: Also, this is the only place where we goto out. All the other
checks individually free the buffer and return directly. I realize that
all the other checks that exit early are errors, but it seems like we
could just return a variable at the end of the function.
> +
> + /*
> + * Retry on any other UNIT ATTENTION occurred.
> + */
> + if (sense_hdr.sense_key == UNIT_ATTENTION) {
> + scsi_print_sense_hdr(sdev, __func__, &sense_hdr);
> + kfree(buff);
> + return -EAGAIN;
> + }
If we get a UNIT ATTENTION, we end up failing scsi_mpath_dev_alloc(),
not retrying. Aside from the comment being wrong, it seems very brittle
to fail here, just because we got a UNIT ATTENTION.
-Ben
> + sdev_printk(KERN_ERR, sdev, "%s: rtpg failed\n",
> + __func__);
> + scsi_print_sense_hdr(sdev, __func__, &sense_hdr);
> + kfree(buff);
> + return -EIO;
> + }
> +
> + len = get_unaligned_be32(&buff[0]) + 4;
> +
> + if (len > bufflen) {
> + /* Resubmit with the correct length */
> + kfree(buff);
> + bufflen = len;
> + buff = kmalloc(bufflen, GFP_KERNEL);
> + if (!buff) {
> + /* Temporary failure, bypass */
> + return -EBUSY;
> + }
> + goto retry;
> + }
> +
> + if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR)
> + tpg_desc_tbl_off = 8;
> + else
> + tpg_desc_tbl_off = 4;
> +
> + for (k = tpg_desc_tbl_off, desc = buff + tpg_desc_tbl_off;
> + k < len;
> + k += off, desc += off) {
> + u16 group_id_found = get_unaligned_be16(&desc[2]);
> +
> + if (group_id_found == group_id) {
> + int valid_states, state, pref;
> +
> + state = desc[0] & 0x0f;
> + pref = desc[0] >> 7;
> + valid_states = desc[1];
> +
> + alua_print_info(sdev, group_id, state, pref,
> valid_states);
> +
> + scsi_mpath_dev->alua_state = state;
> + scsi_mpath_dev->alua_pref = pref;
> + scsi_mpath_dev->alua_valid_states = valid_states;
> + goto out;
> + }
> +
> + off = 8 + (desc[7] * 4);
> + }
> +
> +out:
> + kfree(buff);
> + return 0;
> +}
> +
> int scsi_mpath_dev_alloc(struct scsi_device *sdev)
> {
> struct scsi_mpath_head *scsi_mpath_head;
> - int ret;
> + int ret, tpgs;
>
> if (!scsi_multipath)
> return 0;
>
> - if (!scsi_device_tpgs(sdev) && !scsi_multipath_always) {
> - sdev_printk(KERN_NOTICE, sdev, "tpgs are required for multipath
> support\n");
> + tpgs = alua_check_tpgs(sdev);
> + if (!(tpgs & TPGS_MODE_IMPLICIT) && !scsi_multipath_always) {
> + sdev_printk(KERN_DEBUG, sdev, "IMPLICIT TPGS are required for
> multipath support\n");
> return 0;
> }
>
> @@ -622,6 +765,14 @@ int scsi_mpath_dev_alloc(struct scsi_device *sdev)
> sdev->scsi_mpath_dev->scsi_mpath_head = scsi_mpath_head;
>
> found:
> + if (tpgs & TPGS_MODE_IMPLICIT) {
> + ret = scsi_mpath_alua_init(sdev);
> + if (ret)
> + goto out_put_head;
> + } else {
> + sdev->scsi_mpath_dev->alua_state = SCSI_ACCESS_STATE_OPTIMAL;
> + }
> +
> sdev->scsi_mpath_dev->index = ida_alloc(&scsi_mpath_head->ida,
> GFP_KERNEL);
> if (sdev->scsi_mpath_dev->index < 0) {
> ret = sdev->scsi_mpath_dev->index;
> diff --git a/include/scsi/scsi_multipath.h b/include/scsi/scsi_multipath.h
> index 2011447f482d6..7c7ee2fb7def7 100644
> --- a/include/scsi/scsi_multipath.h
> +++ b/include/scsi/scsi_multipath.h
> @@ -38,6 +38,9 @@ struct scsi_mpath_device {
> int index;
> atomic_t nr_active;
> struct scsi_mpath_head *scsi_mpath_head;
> + int alua_state;
> + int alua_pref;
> + int alua_valid_states;
>
> char device_id_str[SCSI_MPATH_DEVICE_ID_LEN];
> };
> --
> 2.43.5
