[PATCH 3/5] block: introduce preallocate filter

[Vladimir Sementsov-Ogievskiy]

It may be used for file-systems with slow allocation.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block-core.json |   3 +-
 block/preallocate.c  | 255 +++++++++++++++++++++++++++++++++++++++++++
 block/Makefile.objs  |   1 +
 3 files changed, 258 insertions(+), 1 deletion(-)
 create mode 100644 block/preallocate.c

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0e1c6a59f2..a0bda399d6 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2805,7 +2805,7 @@
             'cloop', 'compress', 'copy-on-read', 'dmg', 'file', 'ftp', 'ftps',
             'gluster', 'host_cdrom', 'host_device', 'http', 'https', 'iscsi',
             'luks', 'nbd', 'nfs', 'null-aio', 'null-co', 'nvme', 'parallels',
-            'qcow', 'qcow2', 'qed', 'quorum', 'raw', 'rbd',
+            'preallocate', 'qcow', 'qcow2', 'qed', 'quorum', 'raw', 'rbd',
             { 'name': 'replication', 'if': 'defined(CONFIG_REPLICATION)' },
             'sheepdog',
             'ssh', 'throttle', 'vdi', 'vhdx', 'vmdk', 'vpc', 'vvfat', 'vxhs' ] 
}
@@ -3995,6 +3995,7 @@
       'null-co':    'BlockdevOptionsNull',
       'nvme':       'BlockdevOptionsNVMe',
       'parallels':  'BlockdevOptionsGenericFormat',
+      'preallocate':'BlockdevOptionsGenericFormat',
       'qcow2':      'BlockdevOptionsQcow2',
       'qcow':       'BlockdevOptionsQcow',
       'qed':        'BlockdevOptionsGenericCOWFormat',
diff --git a/block/preallocate.c b/block/preallocate.c
new file mode 100644
index 0000000000..c272a6e41d
--- /dev/null
+++ b/block/preallocate.c
@@ -0,0 +1,255 @@
+/*
+ * preallocate filter driver
+ *
+ * The driver performs preallocate operation: it is injected above
+ * some node, and before each write over EOF it does additional preallocating
+ * write-zeroes request.
+ *
+ * Copyright (c) 2020 Virtuozzo International GmbH.
+ *
+ * Author:
+ *  Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/osdep.h"
+
+#include "qemu/module.h"
+#include "qemu/units.h"
+#include "block/block_int.h"
+
+
+typedef struct BDRVPreallocateState {
+    int64_t prealloc_size;
+    int64_t prealloc_align;
+
+    /*
+     * Track real data end, to crop preallocation on close  data_end may be
+     * negative, which means that actual status is unknown (nothing cropped in
+     * this case)
+     */
+    int64_t data_end;
+} BDRVPreallocateState;
+
+
+static int preallocate_open(BlockDriverState *bs, QDict *options, int flags,
+                            Error **errp)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    /*
+     * Parameters are hardcoded now. May need to add corresponding options in
+     * future.
+     */
+    s->prealloc_align = 1 * MiB;
+    s->prealloc_size = 128 * MiB;
+
+    bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+                               BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
+                               false, errp);
+    if (!bs->file) {
+        return -EINVAL;
+    }
+
+    s->data_end = bdrv_getlength(bs->file->bs);
+    if (s->data_end < 0) {
+        return s->data_end;
+    }
+
+    bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
+        (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
+
+    bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
+        ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
+            bs->file->bs->supported_zero_flags);
+
+    return 0;
+}
+
+static void preallocate_close(BlockDriverState *bs)
+{
+    BDRVPreallocateState *s = bs->opaque;
+
+    if (s->data_end >= 0 && bdrv_getlength(bs->file->bs) > s->data_end) {
+        bdrv_truncate(bs->file, s->data_end, true, PREALLOC_MODE_OFF, 0, NULL);
+    }
+}
+
+static void preallocate_child_perm(BlockDriverState *bs, BdrvChild *c,
+                                   BdrvChildRole role,
+                                   BlockReopenQueue *reopen_queue,
+                                   uint64_t perm, uint64_t shared,
+                                   uint64_t *nperm, uint64_t *nshared)
+{
+    bdrv_default_perms(bs, c, role, reopen_queue, perm, shared, nperm, 
nshared);
+
+    /* Force RESIZE permission, to be able to crop file on close() */
+    *nperm |= BLK_PERM_RESIZE;
+}
+
+static coroutine_fn int preallocate_co_preadv_part(
+        BlockDriverState *bs, uint64_t offset, uint64_t bytes,
+        QEMUIOVector *qiov, size_t qiov_offset, int flags)
+{
+    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
+                               flags);
+}
+
+static int coroutine_fn preallocate_co_pdiscard(BlockDriverState *bs,
+                                               int64_t offset, int bytes)
+{
+    return bdrv_co_pdiscard(bs->file, offset, bytes);
+}
+
+static bool coroutine_fn do_preallocate(BlockDriverState *bs, int64_t offset,
+                                       int64_t bytes, bool write_zero)
+{
+    BDRVPreallocateState *s = bs->opaque;
+    int64_t len, start, end;
+    BdrvTrackedRequest *lock;
+    int ret;
+
+    if (s->data_end >= 0) {
+        s->data_end = MAX(s->data_end,
+                          QEMU_ALIGN_UP(offset + bytes, BDRV_SECTOR_SIZE));
+    }
+
+    len = bdrv_getlength(bs->file->bs);
+    if (len < 0) {
+        return false;
+    }
+
+    if (s->data_end < 0) {
+        s->data_end = MAX(len,
+                          QEMU_ALIGN_UP(offset + bytes, BDRV_SECTOR_SIZE));
+    }
+
+    if (offset + bytes <= len) {
+        return false;
+    }
+
+    lock = bdrv_co_range_try_lock(bs->file->bs, len, INT64_MAX - len);
+    if (!lock) {
+        /* There are already preallocating requests in-fligth */
+        return false;
+    }
+
+    /* Length should not have changed */
+    assert(len == bdrv_getlength(bs->file->bs));
+
+    start = write_zero ? MIN(offset, len) : len;
+    end = QEMU_ALIGN_UP(offset + bytes + s->prealloc_size, s->prealloc_align);
+
+    ret = bdrv_co_pwrite_zeroes_locked(bs->file, start, end - start,
+                                       BDRV_REQ_NO_FALLBACK, lock);
+
+    bdrv_co_range_unlock(lock);
+
+    return !ret;
+}
+
+static int coroutine_fn preallocate_co_pwrite_zeroes(BlockDriverState *bs,
+        int64_t offset, int bytes, BdrvRequestFlags flags)
+{
+    if (do_preallocate(bs, offset, bytes, true)) {
+        return 0;
+    }
+
+    return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
+}
+
+static coroutine_fn int preallocate_co_pwritev_part(BlockDriverState *bs,
+                                                    uint64_t offset,
+                                                    uint64_t bytes,
+                                                    QEMUIOVector *qiov,
+                                                    size_t qiov_offset,
+                                                    int flags)
+{
+    do_preallocate(bs, offset, bytes, false);
+
+    return bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
+                                flags);
+}
+
+static int coroutine_fn
+preallocate_co_truncate(BlockDriverState *bs, int64_t offset,
+                        bool exact, PreallocMode prealloc,
+                        BdrvRequestFlags flags, Error **errp)
+{
+    BDRVPreallocateState *s = bs->opaque;
+    int ret = bdrv_co_truncate(bs->file, offset, exact, prealloc, flags, errp);
+
+    /* s->data_end may become negative here, which means unknown data end */
+    s->data_end = bdrv_getlength(bs->file->bs);
+
+    return ret;
+}
+
+static int coroutine_fn preallocate_co_flush(BlockDriverState *bs)
+{
+    if (!bs->file) {
+        return 0;
+    }
+
+    return bdrv_co_flush(bs->file->bs);
+}
+
+static int64_t preallocate_getlength(BlockDriverState *bs)
+{
+    /*
+     * We probably can return s->data_end here, but seems safer to return real
+     * file length, not trying to hide the preallocation.
+     *
+     * Still, don't miss the chance to restore s->data_end if it is broken.
+     */
+    BDRVPreallocateState *s = bs->opaque;
+    int64_t ret = bdrv_getlength(bs->file->bs);
+
+    if (s->data_end < 0) {
+        s->data_end = ret;
+    }
+
+    return ret;
+}
+
+BlockDriver bdrv_preallocate_filter = {
+    .format_name = "preallocate",
+    .instance_size = sizeof(BDRVPreallocateState),
+
+    .bdrv_getlength = preallocate_getlength,
+    .bdrv_open = preallocate_open,
+    .bdrv_close = preallocate_close,
+
+    .bdrv_co_preadv_part = preallocate_co_preadv_part,
+    .bdrv_co_pwritev_part = preallocate_co_pwritev_part,
+    .bdrv_co_pwrite_zeroes = preallocate_co_pwrite_zeroes,
+    .bdrv_co_pdiscard = preallocate_co_pdiscard,
+    .bdrv_co_flush = preallocate_co_flush,
+    .bdrv_co_truncate = preallocate_co_truncate,
+
+    .bdrv_co_block_status = bdrv_co_block_status_from_file,
+
+    .bdrv_child_perm = preallocate_child_perm,
+
+    .has_variable_length = true,
+    .is_filter = true,
+};
+
+static void bdrv_preallocate_init(void)
+{
+    bdrv_register(&bdrv_preallocate_filter);
+}
+
+block_init(bdrv_preallocate_init);
diff --git a/block/Makefile.objs b/block/Makefile.objs
index 3635b6b4c1..f46a353a35 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -45,6 +45,7 @@ block-obj-y += crypto.o
 block-obj-y += aio_task.o
 block-obj-y += backup-top.o
 block-obj-y += filter-compress.o
+block-obj-y += preallocate.o
 common-obj-y += monitor/
 
 block-obj-y += stream.o
-- 
2.18.0