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_of_bds,
  32                                BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
  33                                false, errp);
  34     if (!bs->file) {
  35         return -EINVAL;
  36     }
  37
  38     bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
  39         (BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
  40
  41     bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
  42         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
  43             bs->file->bs->supported_zero_flags);
  44
  45     return 0;
  46 }
  47
  48
  49 #define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
  50                           | BLK_PERM_WRITE \
  51                           | BLK_PERM_RESIZE)
  52 #define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
  53
  54 static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
  55                            BdrvChildRole role,
  56                            BlockReopenQueue *reopen_queue,
  57                            uint64_t perm, uint64_t shared,
  58                            uint64_t *nperm, uint64_t *nshared)
  59 {
  60     *nperm = perm & PERM_PASSTHROUGH;
  61     *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
  62
  63     /* We must not request write permissions for an inactive node, the child
  64      * cannot provide it. */
  65     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
  66         *nperm |= BLK_PERM_WRITE_UNCHANGED;
  67     }
  68 }
  69
  70
  71 static int64_t cor_getlength(BlockDriverState *bs)
  72 {
  73     return bdrv_getlength(bs->file->bs);
  74 }
  75
  76
  77 static int coroutine_fn cor_co_preadv(BlockDriverState *bs,
  78                                       uint64_t offset, uint64_t bytes,
  79                                       QEMUIOVector *qiov, int flags)
  80 {
  81     return bdrv_co_preadv(bs->file, offset, bytes, qiov,
  82                           flags | BDRV_REQ_COPY_ON_READ);
  83 }
  84
  85
  86 static int coroutine_fn cor_co_pwritev(BlockDriverState *bs,
  87                                        uint64_t offset, uint64_t bytes,
  88                                        QEMUIOVector *qiov, int flags)
  89 {
  90
  91     return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
  92 }
  93
  94
  95 static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
  96                                              int64_t offset, int bytes,
  97                                              BdrvRequestFlags flags)
  98 {
  99     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 100 }
 101
 102
 103 static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
 104                                         int64_t offset, int bytes)
 105 {
 106     return bdrv_co_pdiscard(bs->file, offset, bytes);
 107 }
 108
 109
 110 static void cor_eject(BlockDriverState *bs, bool eject_flag)
 111 {
 112     bdrv_eject(bs->file->bs, eject_flag);
 113 }
 114
 115
 116 static void cor_lock_medium(BlockDriverState *bs, bool locked)
 117 {
 118     bdrv_lock_medium(bs->file->bs, locked);
 119 }
 120
 121
 122 static BlockDriver bdrv_copy_on_read = {
 123     .format_name                        = "copy-on-read",
 124
 125     .bdrv_open                          = cor_open,
 126     .bdrv_child_perm                    = cor_child_perm,
 127
 128     .bdrv_getlength                     = cor_getlength,
 129
 130     .bdrv_co_preadv                     = cor_co_preadv,
 131     .bdrv_co_pwritev                    = cor_co_pwritev,
 132     .bdrv_co_pwrite_zeroes              = cor_co_pwrite_zeroes,
 133     .bdrv_co_pdiscard                   = cor_co_pdiscard,
 134
 135     .bdrv_eject                         = cor_eject,
 136     .bdrv_lock_medium                   = cor_lock_medium,
 137
 138     .bdrv_co_block_status               = bdrv_co_block_status_from_file,
 139
 140     .has_variable_length                = true,
 141     .is_filter                          = true,
 142 };
 143
 144 static void bdrv_copy_on_read_init(void)
 145 {
 146     bdrv_register(&bdrv_copy_on_read);
 147 }
 148
 149 block_init(bdrv_copy_on_read_init);