block/copy-on-read.c

   1 /*
   2  * Copy-on-read filter block driver
   3  *
   4  * Copyright (c) 2018 Red Hat, Inc.
   5  *
   6  * Author:
   7  *   Max Reitz <mreitz@redhat.com>
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License as
  11  * published by the Free Software Foundation; either version 2 or
  12  * (at your option) version 3 of the License.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  21  */
  22
  23 #include "qemu/osdep.h"
  24 #include "block/block_int.h"
  25 #include "qemu/module.h"
  26
  27
  28 static int cor_open(BlockDriverState *bs, QDict *options, int flags,
  29                     Error **errp)
  30 {
  31     bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file, false,
  32                                errp);
  33     if (!bs->file) {
  34         return -EINVAL;
  35     }
  36
  37     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
  38         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
  39
  40     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
  41         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
  42             bs->file->bs->supported_zero_flags);
  43
  44     return 0;
  45 }
  46
  47
  48 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
  49                           | BLK_PERM_WRITE \
  50                           | BLK_PERM_RESIZE)
  51 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
  52
  53 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
  54                            const BdrvChildRole *role,
  55                            BlockReopenQueue *reopen_queue,
  56                            uint64_t perm, uint64_t shared,
  57                            uint64_t *nperm, uint64_t *nshared)
  58 {
  59     *nperm = perm & PERM_PASSTHROUGH;
  60     *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
  61
  62     /* We must not request write permissions for an inactive node, the child
  63      * cannot provide it. */
  64     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
  65         *nperm |= BLK_PERM_WRITE_UNCHANGED;
  66     }
  67 }
  68
  69
  70 static int64_t cor_getlength(BlockDriverState *bs)
  71 {
  72     return bdrv_getlength(bs->file->bs);
  73 }
  74
  75
  76 static int coroutine_fn cor_co_preadv(BlockDriverState *bs,
  77                                       uint64_t offset, uint64_t bytes,
  78                                       QEMUIOVector *qiov, int flags)
  79 {
  80     return bdrv_co_preadv(bs->file, offset, bytes, qiov,
  81                           flags | BDRV_REQ_COPY_ON_READ);
  82 }
  83
  84
  85 static int coroutine_fn cor_co_pwritev(BlockDriverState *bs,
  86                                        uint64_t offset, uint64_t bytes,
  87                                        QEMUIOVector *qiov, int flags)
  88 {
  89
  90     return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
  91 }
  92
  93
  94 static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
  95                                              int64_t offset, int bytes,
  96                                              BdrvRequestFlags flags)
  97 {
  98     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
  99 }
 100
 101
 102 static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
 103                                         int64_t offset, int bytes)
 104 {
 105     return bdrv_co_pdiscard(bs->file, offset, bytes);
 106 }
 107
 108
 109 static void cor_eject(BlockDriverState *bs, bool eject_flag)
 110 {
 111     bdrv_eject(bs->file->bs, eject_flag);
 112 }
 113
 114
 115 static void cor_lock_medium(BlockDriverState *bs, bool locked)
 116 {
 117     bdrv_lock_medium(bs->file->bs, locked);
 118 }
 119
 120
 121 static BlockDriver bdrv_copy_on_read = {
 122     .format_name                        = "copy-on-read",
 123
 124     .bdrv_open                          = cor_open,
 125     .bdrv_child_perm                    = cor_child_perm,
 126
 127     .bdrv_getlength                     = cor_getlength,
 128
 129     .bdrv_co_preadv                     = cor_co_preadv,
 130     .bdrv_co_pwritev                    = cor_co_pwritev,
 131     .bdrv_co_pwrite_zeroes              = cor_co_pwrite_zeroes,
 132     .bdrv_co_pdiscard                   = cor_co_pdiscard,
 133
 134     .bdrv_eject                         = cor_eject,
 135     .bdrv_lock_medium                   = cor_lock_medium,
 136
 137     .bdrv_co_block_status               = bdrv_co_block_status_from_file,
 138
 139     .has_variable_length                = true,
 140     .is_filter                          = true,
 141 };
 142
 143 static void bdrv_copy_on_read_init(void)
 144 {
 145     bdrv_register(&bdrv_copy_on_read);
 146 }
 147
 148 block_init(bdrv_copy_on_read_init);