[V2] 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: Peter Lieven <pl@kamp.de>
---
v1->v2: - add more comments [Fam]
        - free allocmap if allocation of allocmap_valid fails [Fam]
        - fix indent and whitespace errors [Fam]
        - account for cache mode changes on reopen
 block/iscsi.c |  228 ++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 179 insertions(+), 49 deletions(-)

On Fri, 05/20 12:10, Peter Lieven wrote:
> 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.

Looks good to me apart from several wording fixes below.

Reviewed-by: Fam Zheng <famz@redhat.com>

> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
> v1->v2: - add more comments [Fam]
>         - free allocmap if allocation of allocmap_valid fails [Fam]
>         - fix indent and whitespace errors [Fam]
>         - account for cache mode changes on reopen
>  block/iscsi.c |  228 ++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 179 insertions(+), 49 deletions(-)
> 
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 10f3906..e62a9ee 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -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
> @@ -62,7 +62,22 @@ typedef struct IscsiLun {
>      struct scsi_inquiry_logical_block_provisioning lbp;
>      struct scsi_inquiry_block_limits bl;
>      unsigned char *zeroblock;
> -    unsigned long *allocationmap;
> +/* The allocationmap tracks which clusters (pages) on the iSCSI target are

s/allocationmap/allocmap/ to match the post-patch field name?

> + * 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 Qemus information about a page is valid. allocmap tracks if a page is

s/Qemus/QEMU's/

> + * allocated or not. In case Qemus has no valid information about a page the

s/Qemus/QEMU/

> + * 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 its unallocated. */

s/its/it's/ ?

The indentation is a few columes off.

> +    unsigned long *allocmap;
> +    unsigned long *allocmap_valid;
> +    long allocmap_size;
>      int cluster_sectors;
>      bool use_16_for_rw;
>      bool write_protected;
> @@ -415,37 +430,132 @@ static bool is_request_lun_aligned(int64_t sector_num, int nb_sectors,
>      return 1;
>  }
>  
> -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)
>  {
> -    if (iscsilun->allocationmap == NULL) {
> -        return;
> +    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
> +         * threated as invalid to force a relookup of the block

s/threated/treated

> +         * 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;
>      }
> -    bitmap_set(iscsilun->allocationmap,
> -               sector_num / iscsilun->cluster_sectors,
> -               DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +
> +    return 0;
>  }
>  
> -static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
> -                                      int nb_sectors)
> +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) {
> +
> +    if (iscsilun->allocmap == NULL) {
>          return;
>      }
>      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);
> +    if (allocated) {
> +        bitmap_set(iscsilun->allocmap,
> +                   sector_num / iscsilun->cluster_sectors,
> +                   DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +    } else if (nb_clusters > 0) {
> +        bitmap_clear(iscsilun->allocmap, cluster_num, nb_clusters);
> +    }
> +
> +    if (iscsilun->allocmap_valid == NULL) {
> +        return;
>      }
> +    if (valid) {
> +        if (nb_clusters > 0) {
> +            bitmap_set(iscsilun->allocmap_valid, cluster_num, nb_clusters);
> +        }
> +    } else {
> +        bitmap_clear(iscsilun->allocmap_valid,
> +                     sector_num / iscsilun->cluster_sectors,
> +                     DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +    }
> +}
> +
> +static void
> +iscsi_allocmap_set_allocated(IscsiLun *iscsilun, int64_t sector_num,
> +                             int nb_sectors)
> +{
> +    iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, true, true);
> +}
> +
> +static void
> +iscsi_allocmap_set_unallocated(IscsiLun *iscsilun, int64_t sector_num,
> +                               int nb_sectors)
> +{
> +    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
> @@ -507,26 +617,16 @@ 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,
> @@ -611,9 +711,9 @@ 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) {
> @@ -648,16 +748,32 @@ 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, INT_MAX, &pnum, &file);
> +        /* 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,
> +                          INT_MAX, &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;
>          }
> @@ -963,7 +1079,7 @@ retry:
>          return iTask.err_code;
>      }
>  
> -    iscsi_allocationmap_clear(iscsilun, sector_num, nb_sectors);
> +    iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
>  
>      return 0;
>  }
> @@ -1053,13 +1169,14 @@ retry:
>      }
>  
>      if (iTask.status != SCSI_STATUS_GOOD) {
> +        iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
>          return iTask.err_code;
>      }
>  
>      if (flags & BDRV_REQ_MAY_UNMAP) {
> -        iscsi_allocationmap_clear(iscsilun, sector_num, nb_sectors);
> +        iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
>      } else {
> -        iscsi_allocationmap_set(iscsilun, sector_num, nb_sectors);
> +        iscsi_allocmap_set_allocated(iscsilun, sector_num, nb_sectors);
>      }
>  
>      return 0;
> @@ -1633,10 +1750,7 @@ 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);
>          }
>      }
>  
> @@ -1673,7 +1787,7 @@ 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));
>  }
>  
> @@ -1731,6 +1845,14 @@ 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 */
> +    iscsi_allocmap_init(iscsilun, reopen_state->flags);
> +}
> +
>  static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
>  {
>      IscsiLun *iscsilun = bs->opaque;
> @@ -1750,9 +1872,8 @@ 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;
> @@ -1812,6 +1933,13 @@ 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),
> @@ -1835,7 +1963,9 @@ static BlockDriver bdrv_iscsi = {
>      .bdrv_close      = iscsi_close,
>      .bdrv_create     = iscsi_create,
>      .create_opts     = &iscsi_create_opts,
> -    .bdrv_reopen_prepare  = iscsi_reopen_prepare,
> +    .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,
> -- 
> 1.7.9.5
>