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Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf wast
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf waste for extra buf_index adjustment |
Date: |
Fri, 23 Aug 2019 12:06:09 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
(Copying Dan in)
* Wei Yang (address@hidden) wrote:
> In add_to_iovec(), qemu_fflush() will be called if iovec is full. If
> this happens, buf_index is reset. Currently, this is not checked and
> buf_index would always been adjust with buf size.
>
> This is not harmful, but will waste some space in file buffer.
That's a nice find.
> This patch make add_to_iovec() return 1 when it has flushed the file.
> Then the caller could check the return value to see whether it is
> necessary to adjust the buf_index any more.
>
> Signed-off-by: Wei Yang <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
(I wonder if there's a way to wrap that little add_to_iovec, check, add
to index, flush in a little wrapper).
Dave
> ---
> migration/qemu-file.c | 42 ++++++++++++++++++++++++++++--------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 35c22605dd..05d9f42ddb 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -343,8 +343,16 @@ int qemu_fclose(QEMUFile *f)
> return ret;
> }
>
> -static void add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
> - bool may_free)
> +/*
> + * Add buf to iovec. Do flush if iovec is full.
> + *
> + * Return values:
> + * 1 iovec is full and flushed
> + * 0 iovec is not flushed
> + *
> + */
> +static int add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
> + bool may_free)
> {
> /* check for adjacent buffer and coalesce them */
> if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
> @@ -362,7 +370,10 @@ static void add_to_iovec(QEMUFile *f, const uint8_t
> *buf, size_t size,
>
> if (f->iovcnt >= MAX_IOV_SIZE) {
> qemu_fflush(f);
> + return 1;
> }
> +
> + return 0;
> }
>
> void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
> @@ -391,10 +402,11 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf,
> size_t size)
> }
> memcpy(f->buf + f->buf_index, buf, l);
> f->bytes_xfer += l;
> - add_to_iovec(f, f->buf + f->buf_index, l, false);
> - f->buf_index += l;
> - if (f->buf_index == IO_BUF_SIZE) {
> - qemu_fflush(f);
> + if (!add_to_iovec(f, f->buf + f->buf_index, l, false)) {
> + f->buf_index += l;
> + if (f->buf_index == IO_BUF_SIZE) {
> + qemu_fflush(f);
> + }
> }
> if (qemu_file_get_error(f)) {
> break;
> @@ -412,10 +424,11 @@ void qemu_put_byte(QEMUFile *f, int v)
>
> f->buf[f->buf_index] = v;
> f->bytes_xfer++;
> - add_to_iovec(f, f->buf + f->buf_index, 1, false);
> - f->buf_index++;
> - if (f->buf_index == IO_BUF_SIZE) {
> - qemu_fflush(f);
> + if (!add_to_iovec(f, f->buf + f->buf_index, 1, false)) {
> + f->buf_index++;
> + if (f->buf_index == IO_BUF_SIZE) {
> + qemu_fflush(f);
> + }
> }
> }
>
> @@ -717,10 +730,11 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream
> *stream,
> }
>
> qemu_put_be32(f, blen);
> - add_to_iovec(f, f->buf + f->buf_index, blen, false);
> - f->buf_index += blen;
> - if (f->buf_index == IO_BUF_SIZE) {
> - qemu_fflush(f);
> + if (!add_to_iovec(f, f->buf + f->buf_index, blen, false)) {
> + f->buf_index += blen;
> + if (f->buf_index == IO_BUF_SIZE) {
> + qemu_fflush(f);
> + }
> }
> return blen + sizeof(int32_t);
> }
> --
> 2.17.1
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf waste for extra buf_index adjustment,
Dr. David Alan Gilbert <=