Hi Marco,
On 2025-10-01 18:18, Marco Cavenati wrote:
> Enable the use of the mapped-ram migration feature with savevm/loadvm
> snapshots by adding the QIO_CHANNEL_FEATURE_SEEKABLE feature to
> QIOChannelBlock. Implement io_preadv and io_pwritev methods to provide
> positioned I/O capabilities that don't modify the channel's position
> pointer.
>
> Signed-off-by: Marco Cavenati <[email protected]>
> ---
> migration/channel-block.c | 48 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 48 insertions(+)
>
> diff --git a/migration/channel-block.c b/migration/channel-block.c
> index 97de5a691b..30dcefcd8e 100644
> --- a/migration/channel-block.c
> +++ b/migration/channel-block.c
> @@ -30,6 +30,7 @@ qio_channel_block_new(BlockDriverState *bs)
> QIOChannelBlock *ioc;
>
> ioc = QIO_CHANNEL_BLOCK(object_new(TYPE_QIO_CHANNEL_BLOCK));
> + qio_channel_set_feature(QIO_CHANNEL(ioc), QIO_CHANNEL_FEATURE_SEEKABLE);
>
> bdrv_ref(bs);
> ioc->bs = bs;
> @@ -96,6 +97,49 @@ qio_channel_block_writev(QIOChannel *ioc,
> return qiov.size;
> }
>
> +#ifdef CONFIG_PREADV
I don't think this conditional macro is necessary here. QIOChannelFile
needs it because it directly uses preadv() syscall which might not be
available on all systems (see when CONFIG_PREADV is defined below).
config_host_data.set('CONFIG_PREADV', cc.has_function('preadv', prefix:
'#include <sys/uio.h>'))
However, bdrv_readv_vmstate() (wrapper of bdrv_co_readv_vmstate())
should be always available IUUC (it is not conditionally compiled based
on if preadv() syscall is available).
> +static ssize_t
> +qio_channel_block_preadv(QIOChannel *ioc,
> + const struct iovec *iov,
> + size_t niov,
> + off_t offset,
> + Error **errp)
> +{
> + QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
> + QEMUIOVector qiov;
> + int ret;
> +
> + qemu_iovec_init_external(&qiov, (struct iovec *)iov, niov);
> + ret = bdrv_readv_vmstate(bioc->bs, &qiov, offset);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "bdrv_readv_vmstate failed");
> + return -1;
> + }
> +
> + return qiov.size;
> +}
> +
> +static ssize_t
> +qio_channel_block_pwritev(QIOChannel *ioc,
> + const struct iovec *iov,
> + size_t niov,
> + off_t offset,
> + Error **errp)
> +{
> + QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
> + QEMUIOVector qiov;
> + int ret;
> +
> + qemu_iovec_init_external(&qiov, (struct iovec *)iov, niov);
> + ret = bdrv_writev_vmstate(bioc->bs, &qiov, offset);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "bdrv_writev_vmstate failed");
> + return -1;
> + }
> +
> + return qiov.size;
> +}
> +#endif /* CONFIG_PREADV */
>
> static int
> qio_channel_block_set_blocking(QIOChannel *ioc,
> @@ -177,6 +221,10 @@ qio_channel_block_class_init(ObjectClass *klass,
> ioc_klass->io_writev = qio_channel_block_writev;
> ioc_klass->io_readv = qio_channel_block_readv;
> ioc_klass->io_set_blocking = qio_channel_block_set_blocking;
> +#ifdef CONFIG_PREADV
> + ioc_klass->io_preadv = qio_channel_block_preadv;
> + ioc_klass->io_pwritev = qio_channel_block_pwritev;
> +#endif
> ioc_klass->io_seek = qio_channel_block_seek;
> ioc_klass->io_close = qio_channel_block_close;
> ioc_klass->io_set_aio_fd_handler = qio_channel_block_set_aio_fd_handler;
> --
> 2.48.1
>
Best regards,
Juraj Marcin
