Re: [Qemu-devel] [PATCH v5 07/11] curl: make use of CURLDataCache.

[Fam Zheng <famz@redhat.com>]

On Thu, 05/23 16:23, Stefan Hajnoczi wrote:
> On Thu, May 23, 2013 at 11:38:05AM +0800, Fam Zheng wrote:
> > @@ -221,31 +215,35 @@ static void curl_complete_io(BDRVCURLState *bs, CURLAIOCB *acb,
> >  
> >  static size_t curl_read_cb(void *ptr, size_t size, size_t nmemb, void *opaque)
> >  {
> > -    CURLState *s = ((CURLState*)opaque);
> > +    CURLState *s = (CURLState *)opaque;
> 
> You can drop the cast completely because opaque is void*.
> 
> > +    CURLDataCache *c = s->cache;
> >      size_t realsize = size * nmemb;
> > -    int i;
> > -
> > -    DPRINTF("CURL: Just reading %zd bytes\n", realsize);
> > +    CURLAIOCB *acb;
> >  
> > -    if (!s || !s->orig_buf)
> > +    if (!c || !c->data) {
> >          goto read_end;
> > +    }
> > +    if (c->write_pos >= c->data_len) {
> > +        goto read_end;
> > +    }
> > +    memcpy(c->data + c->write_pos, ptr,
> > +           MIN(realsize, c->data_len - c->write_pos));
> > +    c->write_pos += realsize;
> > +    if (c->write_pos >= c->data_len) {
> > +        c->write_pos = c->data_len;
> > +    }
> >  
> > -    memcpy(s->orig_buf + s->buf_off, ptr, realsize);
> > -    s->buf_off += realsize;
> 
> Why did you add MIN(realsize, c->data_len - c->write_pos)?  The original
> code trusts realsize to be within s->orig_buf.

I don't see an evidence why it's safe here. CURL certainly doesn't know
how much buffer do we have. (man 3 curl_easy_setopt, section
CURLOPT_WRITEFUNCTION)

> 
> > -
> > -    for(i=0; i<CURL_NUM_ACB; i++) {
> > -        CURLAIOCB *acb = s->acb[i];
> > -
> > -        if (!acb)
> > -            continue;
> > -
> > -        if ((s->buf_off >= acb->end)) {
> > -            qemu_iovec_from_buf(acb->qiov, 0, s->orig_buf + acb->start,
> > -                                acb->end - acb->start);
> > -            acb->common.cb(acb->common.opaque, 0);
> > -            qemu_aio_release(acb);
> > -            s->acb[i] = NULL;
> > +    acb = QLIST_FIRST(&s->s->acbs);
> > +    while (acb) {
> > +        size_t aio_base = acb->sector_num * SECTOR_SIZE;
> 
> int64_t
> 
> > @@ -600,29 +596,41 @@ static void curl_readv_bh_cb(void *p)
> >      // No cache found, so let's start a new request
> >      state = curl_init_state(s);
> >      if (!state) {
> > -        acb->common.cb(acb->common.opaque, -EIO);
> > -        qemu_aio_release(acb);
> > -        return;
> > +        goto err_release;
> >      }
> >  
> > -    acb->start = 0;
> > -    acb->end = (acb->nb_sectors * SECTOR_SIZE);
> > -
> > -    state->buf_off = 0;
> > -    if (state->orig_buf)
> > -        g_free(state->orig_buf);
> > -    state->buf_start = start;
> > -    state->buf_len = acb->end + s->readahead_size;
> > -    end = MIN(start + state->buf_len, s->len) - 1;
> > -    state->orig_buf = g_malloc(state->buf_len);
> > -    state->acb[0] = acb;
> > -
> > -    snprintf(state->range, sizeof(state->range) - 1, "%zd-%zd", start, end);
> > -    DPRINTF("CURL (AIO): Reading %d at %zd (%s)\n",
> > -            (acb->nb_sectors * SECTOR_SIZE), start, state->range);
> > -    curl_easy_setopt(state->curl, CURLOPT_RANGE, state->range);
> > +    cache = g_malloc0(sizeof(CURLDataCache));
> > +    cache->base_pos = acb->sector_num * SECTOR_SIZE;
> > +    cache->data_len = aio_bytes + s->readahead_size;
> > +    cache->write_pos = 0;
> > +    cache->data = g_malloc(cache->data_len);
> >  
> > +    QLIST_INSERT_HEAD(&s->acbs, acb, next);
> > +    snprintf(state->range, sizeof(state->range) - 1, "%zd-%zd", cache->base_pos,
> > +             cache->base_pos + cache->data_len);
> > +    DPRINTF("Reading range: %s\n", state->range);
> > +    curl_easy_setopt(state->curl, CURLOPT_RANGE, state->range);
> > +    QLIST_INSERT_HEAD(&s->cache, cache, next);
> > +    state->cache = cache;
> > +    cache->use_count++;
> 
> I don't see where you bump the use_count when a cache lookup is
> successful.  Maybe I just missed it in the other patches.

Use count is for serving as the receiving buffer for submitted CURL
requests. It's not necessary to bump use_count when cache lookup is
successful, since data is immediately copied to guest, no ref to the
cache hold.

-- 
Fam