Commit e1123a3b authored by Peter Lieven's avatar Peter Lieven Committed by Paolo Bonzini
Browse files

block/iscsi: allow caching of the allocation map 



until now the allocation map was used only as a hint if a cluster
is allocated or not. If a block was not allocated (or Qemu had
no info about the allocation status) a get_block_status call was
issued to check the allocation status and possibly avoid
a subsequent read of unallocated sectors. If a block known to be
allocated the get_block_status call was omitted. In the other case
a get_block_status call was issued before every read to avoid
the necessity for a consistent allocation map. To avoid the
potential overhead of calling get_block_status for each and
every read request this took only place for the bigger requests.

This patch enhances this mechanism to cache the allocation
status and avoid calling get_block_status for blocks where
the allocation status has been queried before. This allows
for bypassing the read request even for smaller requests and
additionally omits calling get_block_status for known to be
unallocated blocks.

Signed-off-by: default avatarPeter Lieven <pl@kamp.de>
Message-Id: <1468831940-15556-3-git-send-email-pl@kamp.de>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent eb36b953

block/iscsi.c

+192 −58
Original line number Diff line number Diff line
@@ -2,7 +2,7 @@ 
 * QEMU Block driver for iSCSI images

 *

 * Copyright (c) 2010-2011 Ronnie Sahlberg <ronniesahlberg@gmail.com>

 * Copyright (c) 2012-2015 Peter Lieven <pl@kamp.de>

 * Copyright (c) 2012-2016 Peter Lieven <pl@kamp.de>

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal
@@ -61,7 +61,23 @@ typedef struct IscsiLun { 
    struct scsi_inquiry_logical_block_provisioning lbp;

    struct scsi_inquiry_block_limits bl;

    unsigned char *zeroblock;

    unsigned long *allocationmap;

    /* The allocmap tracks which clusters (pages) on the iSCSI target are

     * allocated and which are not. In case a target returns zeros for

     * unallocated pages (iscsilun->lprz) we can directly return zeros instead

     * of reading zeros over the wire if a read request falls within an

     * unallocated block. As there are 3 possible states we need 2 bitmaps to

     * track. allocmap_valid keeps track if QEMU's information about a page is

     * valid. allocmap tracks if a page is allocated or not. In case QEMU has no

     * valid information about a page the corresponding allocmap entry should be

     * switched to unallocated as well to force a new lookup of the allocation

     * status as lookups are generally skipped if a page is suspect to be

     * allocated. If a iSCSI target is opened with cache.direct = on the

     * allocmap_valid does not exist turning all cached information invalid so

     * that a fresh lookup is made for any page even if allocmap entry returns

     * it's unallocated. */

    unsigned long *allocmap;

    unsigned long *allocmap_valid;

    long allocmap_size;

    int cluster_sectors;

    bool use_16_for_rw;

    bool write_protected;
@@ -422,41 +438,137 @@ static bool is_sector_request_lun_aligned(int64_t sector_num, int nb_sectors, 
                                       iscsilun);

}



static unsigned long *iscsi_allocationmap_init(IscsiLun *iscsilun)

static void iscsi_allocmap_free(IscsiLun *iscsilun)

{

    return bitmap_try_new(DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks,

                                                       iscsilun),

                                       iscsilun->cluster_sectors));

    g_free(iscsilun->allocmap);

    g_free(iscsilun->allocmap_valid);

    iscsilun->allocmap = NULL;

    iscsilun->allocmap_valid = NULL;

}



static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,

                                    int nb_sectors)



static int iscsi_allocmap_init(IscsiLun *iscsilun, int open_flags)

{

    iscsi_allocmap_free(iscsilun);



    iscsilun->allocmap_size =

        DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks, iscsilun),

                     iscsilun->cluster_sectors);



    iscsilun->allocmap = bitmap_try_new(iscsilun->allocmap_size);

    if (!iscsilun->allocmap) {

        return -ENOMEM;

    }



    if (open_flags & BDRV_O_NOCACHE) {

        /* in case that cache.direct = on all allocmap entries are

         * treated as invalid to force a relookup of the block

         * status on every read request */

        return 0;

    }



    iscsilun->allocmap_valid = bitmap_try_new(iscsilun->allocmap_size);

    if (!iscsilun->allocmap_valid) {

        /* if we are under memory pressure free the allocmap as well */

        iscsi_allocmap_free(iscsilun);

        return -ENOMEM;

    }



    return 0;

}



static void

iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,

                      int nb_sectors, bool allocated, bool valid)

{

    int64_t cluster_num, nb_clusters;

    if (iscsilun->allocationmap == NULL) {

    int64_t cl_num_expanded, nb_cls_expanded, cl_num_shrunk, nb_cls_shrunk;



    if (iscsilun->allocmap == NULL) {

        return;

    }

    cluster_num = sector_num / iscsilun->cluster_sectors;

    nb_clusters = DIV_ROUND_UP(sector_num + nb_sectors,

                               iscsilun->cluster_sectors) - cluster_num;

    bitmap_set(iscsilun->allocationmap, cluster_num, nb_clusters);

    /* expand to entirely contain all affected clusters */

    cl_num_expanded = sector_num / iscsilun->cluster_sectors;

    nb_cls_expanded = DIV_ROUND_UP(sector_num + nb_sectors,

                                   iscsilun->cluster_sectors) - cl_num_expanded;

    /* shrink to touch only completely contained clusters */

    cl_num_shrunk = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);

    nb_cls_shrunk = (sector_num + nb_sectors) / iscsilun->cluster_sectors

                      - cl_num_shrunk;

    if (allocated) {

        bitmap_set(iscsilun->allocmap, cl_num_expanded, nb_cls_expanded);

    } else {

        bitmap_clear(iscsilun->allocmap, cl_num_shrunk, nb_cls_shrunk);

    }



static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,

    if (iscsilun->allocmap_valid == NULL) {

        return;

    }

    if (valid) {

        bitmap_set(iscsilun->allocmap_valid, cl_num_shrunk, nb_cls_shrunk);

    } else {

        bitmap_clear(iscsilun->allocmap_valid, cl_num_expanded,

                     nb_cls_expanded);

    }

}



static void

iscsi_allocmap_set_allocated(IscsiLun *iscsilun, int64_t sector_num,

                             int nb_sectors)

{

    int64_t cluster_num, nb_clusters;

    if (iscsilun->allocationmap == NULL) {

        return;

    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, true, true);

}

    cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);

    nb_clusters = (sector_num + nb_sectors) / iscsilun->cluster_sectors

                  - cluster_num;

    if (nb_clusters > 0) {

        bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);



static void

iscsi_allocmap_set_unallocated(IscsiLun *iscsilun, int64_t sector_num,

                               int nb_sectors)

{

    /* Note: if cache.direct=on the fifth argument to iscsi_allocmap_update

     * is ignored, so this will in effect be an iscsi_allocmap_set_invalid.

     */

    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, true);

}



static void iscsi_allocmap_set_invalid(IscsiLun *iscsilun, int64_t sector_num,

                                       int nb_sectors)

{

    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, false);

}



static void iscsi_allocmap_invalidate(IscsiLun *iscsilun)

{

    if (iscsilun->allocmap) {

        bitmap_zero(iscsilun->allocmap, iscsilun->allocmap_size);

    }

    if (iscsilun->allocmap_valid) {

        bitmap_zero(iscsilun->allocmap_valid, iscsilun->allocmap_size);

    }

}



static inline bool

iscsi_allocmap_is_allocated(IscsiLun *iscsilun, int64_t sector_num,

                            int nb_sectors)

{

    unsigned long size;

    if (iscsilun->allocmap == NULL) {

        return true;

    }

    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);

    return !(find_next_bit(iscsilun->allocmap, size,

                           sector_num / iscsilun->cluster_sectors) == size);

}



static inline bool iscsi_allocmap_is_valid(IscsiLun *iscsilun,

                                           int64_t sector_num, int nb_sectors)

{

    unsigned long size;

    if (iscsilun->allocmap_valid == NULL) {

        return false;

    }

    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);

    return (find_next_zero_bit(iscsilun->allocmap_valid, size,

                               sector_num / iscsilun->cluster_sectors) == size);

}



static int coroutine_fn

iscsi_co_writev_flags(BlockDriverState *bs, int64_t sector_num, int nb_sectors,

                      QEMUIOVector *iov, int flags)
@@ -517,26 +629,16 @@ retry: 
    }



    if (iTask.status != SCSI_STATUS_GOOD) {

        iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);

        return iTask.err_code;

    }



    iscsi_allocationmap_set(iscsilun, sector_num, nb_sectors);

    iscsi_allocmap_set_allocated(iscsilun, sector_num, nb_sectors);



    return 0;

}





static bool iscsi_allocationmap_is_allocated(IscsiLun *iscsilun,

                                             int64_t sector_num, int nb_sectors)

{

    unsigned long size;

    if (iscsilun->allocationmap == NULL) {

        return true;

    }

    size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);

    return !(find_next_bit(iscsilun->allocationmap, size,

                           sector_num / iscsilun->cluster_sectors) == size);

}



static int64_t coroutine_fn iscsi_co_get_block_status(BlockDriverState *bs,

                                                  int64_t sector_num,
@@ -621,9 +723,9 @@ retry: 
    }



    if (ret & BDRV_BLOCK_ZERO) {

        iscsi_allocationmap_clear(iscsilun, sector_num, *pnum);

        iscsi_allocmap_set_unallocated(iscsilun, sector_num, *pnum);

    } else {

        iscsi_allocationmap_set(iscsilun, sector_num, *pnum);

        iscsi_allocmap_set_allocated(iscsilun, sector_num, *pnum);

    }



    if (*pnum > nb_sectors) {
@@ -659,17 +761,32 @@ static int coroutine_fn iscsi_co_readv(BlockDriverState *bs, 
        return -EINVAL;

    }



    if (iscsilun->lbprz && nb_sectors >= ISCSI_CHECKALLOC_THRES &&

        !iscsi_allocationmap_is_allocated(iscsilun, sector_num, nb_sectors)) {

        int64_t ret;

    /* if cache.direct is off and we have a valid entry in our allocation map

     * we can skip checking the block status and directly return zeroes if

     * the request falls within an unallocated area */

    if (iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&

        !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {

            qemu_iovec_memset(iov, 0, 0x00, iov->size);

            return 0;

    }



    if (nb_sectors >= ISCSI_CHECKALLOC_THRES &&

        !iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&

        !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {

        int pnum;

        BlockDriverState *file;

        ret = iscsi_co_get_block_status(bs, sector_num,

        /* check the block status from the beginning of the cluster

         * containing the start sector */

        int64_t ret = iscsi_co_get_block_status(bs,

                          sector_num - sector_num % iscsilun->cluster_sectors,

                          BDRV_REQUEST_MAX_SECTORS, &pnum, &file);

        if (ret < 0) {

            return ret;

        }

        if (ret & BDRV_BLOCK_ZERO && pnum >= nb_sectors) {

        /* if the whole request falls into an unallocated area we can avoid

         * to read and directly return zeroes instead */

        if (ret & BDRV_BLOCK_ZERO &&

            pnum >= nb_sectors + sector_num % iscsilun->cluster_sectors) {

            qemu_iovec_memset(iov, 0, 0x00, iov->size);

            return 0;

        }
@@ -983,7 +1100,7 @@ retry: 
        return iTask.err_code;

    }



    iscsi_allocationmap_clear(iscsilun, sector_num, nb_sectors);

    iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);



    return 0;

}
@@ -1073,14 +1190,16 @@ retry: 
    }



    if (iTask.status != SCSI_STATUS_GOOD) {

        iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,

                                   count >> BDRV_SECTOR_BITS);

        return iTask.err_code;

    }



    if (flags & BDRV_REQ_MAY_UNMAP) {

        iscsi_allocationmap_clear(iscsilun, offset >> BDRV_SECTOR_BITS,

        iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,

                                   count >> BDRV_SECTOR_BITS);

    } else {

        iscsi_allocationmap_set(iscsilun, offset >> BDRV_SECTOR_BITS,

        iscsi_allocmap_set_allocated(iscsilun, offset >> BDRV_SECTOR_BITS,

                                     count >> BDRV_SECTOR_BITS);

    }
@@ -1654,10 +1773,7 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags, 
        iscsilun->cluster_sectors = (iscsilun->bl.opt_unmap_gran *

                                     iscsilun->block_size) >> BDRV_SECTOR_BITS;

        if (iscsilun->lbprz) {

            iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);

            if (iscsilun->allocationmap == NULL) {

                ret = -ENOMEM;

            }

            ret = iscsi_allocmap_init(iscsilun, bs->open_flags);

        }

    }
@@ -1694,7 +1810,7 @@ static void iscsi_close(BlockDriverState *bs) 
    }

    iscsi_destroy_context(iscsi);

    g_free(iscsilun->zeroblock);

    g_free(iscsilun->allocationmap);

    iscsi_allocmap_free(iscsilun);

    memset(iscsilun, 0, sizeof(IscsiLun));

}
@@ -1758,6 +1874,16 @@ static int iscsi_reopen_prepare(BDRVReopenState *state, 
    return 0;

}



static void iscsi_reopen_commit(BDRVReopenState *reopen_state)

{

    IscsiLun *iscsilun = reopen_state->bs->opaque;



    /* the cache.direct status might have changed */

    if (iscsilun->allocmap != NULL) {

        iscsi_allocmap_init(iscsilun, reopen_state->flags);

    }

}



static int iscsi_truncate(BlockDriverState *bs, int64_t offset)

{

    IscsiLun *iscsilun = bs->opaque;
@@ -1777,9 +1903,8 @@ static int iscsi_truncate(BlockDriverState *bs, int64_t offset) 
        return -EINVAL;

    }



    if (iscsilun->allocationmap != NULL) {

        g_free(iscsilun->allocationmap);

        iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);

    if (iscsilun->allocmap != NULL) {

        iscsi_allocmap_init(iscsilun, bs->open_flags);

    }



    return 0;
@@ -1839,6 +1964,13 @@ static int iscsi_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) 
    return 0;

}



static void iscsi_invalidate_cache(BlockDriverState *bs,

                                   Error **errp)

{

    IscsiLun *iscsilun = bs->opaque;

    iscsi_allocmap_invalidate(iscsilun);

}



static QemuOptsList iscsi_create_opts = {

    .name = "iscsi-create-opts",

    .head = QTAILQ_HEAD_INITIALIZER(iscsi_create_opts.head),
@@ -1863,6 +1995,8 @@ static BlockDriver bdrv_iscsi = { 
    .bdrv_create     = iscsi_create,

    .create_opts     = &iscsi_create_opts,

    .bdrv_reopen_prepare   = iscsi_reopen_prepare,

    .bdrv_reopen_commit    = iscsi_reopen_commit,

    .bdrv_invalidate_cache = iscsi_invalidate_cache,



    .bdrv_getlength  = iscsi_getlength,

    .bdrv_get_info   = iscsi_get_info,