[Qemu-devel] [PATCH] block/iscsi: allow caching of the allocation map

[Peter Lieven <pl@kamp.de>]

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>
---
 block/iscsi.c | 194 +++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 144 insertions(+), 50 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 10f3906..b25bebd 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 +62,9 @@ typedef struct IscsiLun {
     struct scsi_inquiry_logical_block_provisioning lbp;
     struct scsi_inquiry_block_limits bl;
     unsigned char *zeroblock;
-    unsigned long *allocationmap;
+    unsigned long *allocmap;
+    unsigned long *allocmap_valid;
+    long allocmap_size;
     int cluster_sectors;
     bool use_16_for_rw;
     bool write_protected;
@@ -415,39 +417,127 @@ 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;
+    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) {
+        return 0;
+    }
+
+    iscsilun->allocmap_valid = bitmap_try_new(iscsilun->allocmap_size);
+    if (!iscsilun->allocmap_valid) {
+        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
 iscsi_co_writev_flags(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
                       QEMUIOVector *iov, int flags)
@@ -507,26 +597,16 @@ 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 +691,9 @@ 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) {
@@ -629,7 +709,7 @@ out:
     return ret;
 }
 
-static int coroutine_fn iscsi_co_readv(BlockDriverState *bs,
+ static int coroutine_fn iscsi_co_readv(BlockDriverState *bs,
                                        int64_t sector_num, int nb_sectors,
                                        QEMUIOVector *iov)
 {
@@ -648,16 +728,25 @@ 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 (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);
+        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 (ret & BDRV_BLOCK_ZERO &&
+            pnum >= nb_sectors + sector_num % iscsilun->cluster_sectors) {
             qemu_iovec_memset(iov, 0, 0x00, iov->size);
             return 0;
         }
@@ -892,7 +981,6 @@ static BlockAIOCB *iscsi_aio_ioctl(BlockDriverState *bs,
     }
 
     iscsi_set_events(iscsilun);
-
     return &acb->common;
 }
 
@@ -963,7 +1051,7 @@ 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 +1141,14 @@ 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 +1722,7 @@ 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 +1759,7 @@ 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));
 }
 
@@ -1750,9 +1836,9 @@ 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_free(iscsilun);
+        iscsi_allocmap_init(iscsilun, bs->open_flags);
     }
 
     return 0;
@@ -1812,6 +1898,13 @@ 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),
@@ -1836,6 +1929,7 @@ static BlockDriver bdrv_iscsi = {
     .bdrv_create     = iscsi_create,
     .create_opts     = &iscsi_create_opts,
     .bdrv_reopen_prepare  = iscsi_reopen_prepare,
+    .bdrv_invalidate_cache = iscsi_invalidate_cache,
 
     .bdrv_getlength  = iscsi_getlength,
     .bdrv_get_info   = iscsi_get_info,
-- 
1.9.1