Commit cd219eb1 authored by Max Reitz's avatar Max Reitz Committed by Kevin Wolf
Browse files

block/null-{co,aio}: Allow reading zeroes 



This is optional so that it does not impede the null block driver's
performance unless this behavior is desired.

Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Acked-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent aad15de4

block/null.c

+20 −0
Original line number Diff line number Diff line
@@ -15,10 +15,12 @@ 
#include "block/block_int.h"



#define NULL_OPT_LATENCY "latency-ns"

#define NULL_OPT_ZEROES  "read-zeroes"



typedef struct {

    int64_t length;

    int64_t latency_ns;

    bool read_zeroes;

} BDRVNullState;



static QemuOptsList runtime_opts = {
@@ -41,6 +43,11 @@ static QemuOptsList runtime_opts = { 
            .help = "nanoseconds (approximated) to wait "

                    "before completing request",

        },

        {

            .name = NULL_OPT_ZEROES,

            .type = QEMU_OPT_BOOL,

            .help = "return zeroes when read",

        },

        { /* end of list */ }

    },

};
@@ -62,6 +69,7 @@ static int null_file_open(BlockDriverState *bs, QDict *options, int flags, 
        error_setg(errp, "latency-ns is invalid");

        ret = -EINVAL;

    }

    s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);

    qemu_opts_del(opts);

    return ret;

}
@@ -91,6 +99,12 @@ static coroutine_fn int null_co_readv(BlockDriverState *bs, 
                                      int64_t sector_num, int nb_sectors,

                                      QEMUIOVector *qiov)

{

    BDRVNullState *s = bs->opaque;



    if (s->read_zeroes) {

        qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);

    }



    return null_co_common(bs);

}
@@ -160,6 +174,12 @@ static BlockAIOCB *null_aio_readv(BlockDriverState *bs, 
                                  BlockCompletionFunc *cb,

                                  void *opaque)

{

    BDRVNullState *s = bs->opaque;



    if (s->read_zeroes) {

        qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);

    }



    return null_aio_common(bs, cb, opaque);

}