[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf wast
From: |
Wei Yang |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] migration/qemu-file: fix potential buf waste for extra buf_index adjustment |
Date: |
Wed, 11 Sep 2019 12:26:23 +0000 |
User-agent: |
NeoMutt/20170113 (1.7.2) |
On Tue, Sep 03, 2019 at 07:43:24PM +0100, Dr. David Alan Gilbert wrote:
>* Wei Yang (address@hidden) wrote:
>> On Fri, Aug 23, 2019 at 12:06:09PM +0100, Dr. David Alan Gilbert wrote:
>> >(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);
>> >> + }
>>
>> You mean put these four lines into a wrapper?
>>
>> Name it as add_buf_to_iovec?
>
>Yes.
Sure, Let me prepare v2 with this.
--
Wei Yang
Help you, Help me