[Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Nolan]

Allow adjustment of http block device's readahead size, via the
environment variable "HTTP_READAHEAD_SIZE".

Signed-off-by: Nolan Leake <nolan <at> sigbus.net>

diff --git a/block/curl.c b/block/curl.c
index e1a553f..32530eb 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -24,6 +24,7 @@
 #include "qemu-common.h"
 #include "block_int.h"
 #include <curl/curl.h>
+#include <stdlib.h>
 
 // #define DEBUG
 // #define DEBUG_VERBOSE
@@ -71,6 +72,7 @@ typedef struct BDRVCURLState {
     size_t len;
     CURLState states[CURL_NUM_STATES];
     char *url;
+    size_t readahead_size;
 } BDRVCURLState;
 
 static void curl_clean_state(CURLState *s);
@@ -298,9 +300,21 @@ static int curl_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVCURLState *s = bs->opaque;
     CURLState *state = NULL;
+    char *readahead;
     double d;
     static int inited = 0;
 
+    s->readahead_size = READ_AHEAD_SIZE;
+    readahead = getenv("HTTP_READAHEAD_SIZE");
+    if (readahead) {
+        s->readahead_size = atoi(readahead);
+    }
+    if ((s->readahead_size & 0x1ff) != 0) {
+        fprintf(stderr, "HTTP_READAHEAD_SIZE %Zd not a multiple of 512\n",
+                s->readahead_size);
+        goto out_noclean;
+    }
+
     if (!inited) {
         curl_global_init(CURL_GLOBAL_ALL);
         inited = 1;
@@ -346,6 +360,7 @@ out:
     curl_easy_cleanup(state->curl);
     state->curl = NULL;
 out_noclean:
+    qemu_free(s->url);
     return -EINVAL;
 }
 
@@ -401,7 +416,7 @@ static BlockDriverAIOCB *curl_aio_readv(BlockDriverState *bs,
     if (state->orig_buf)
         qemu_free(state->orig_buf);
     state->buf_start = start;
-    state->buf_len = acb->end + READ_AHEAD_SIZE;
+    state->buf_len = acb->end + s->readahead_size;
     end = MIN(start + state->buf_len, s->len) - 1;
     state->orig_buf = qemu_malloc(state->buf_len);
     state->acb[0] = acb;

Re: [Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Anthony Liguori]

Nolan wrote:
> Allow adjustment of http block device's readahead size, via the
> environment variable "HTTP_READAHEAD_SIZE".
>
> Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
>   

I'd rather a command line option than an environmental variable.

Regards,

Anthony Liguori

Re: [Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Alexander Graf]

On 29.06.2009, at 15:45, Anthony Liguori wrote:

> Nolan wrote:
>> Allow adjustment of http block device's readahead size, via the
>> environment variable "HTTP_READAHEAD_SIZE".
>>
>> Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
>>
>
> I'd rather a command line option than an environmental variable.

Wouldn't it make sense to pass arbitrary options via -drive to backends?

That way we could have -drive file=http://sample.com/test.iso,http-readahead=1024 
.

Alex

Re: [Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Anthony Liguori]

Alexander Graf wrote:
>
> On 29.06.2009, at 15:45, Anthony Liguori wrote:
>
>> Nolan wrote:
>>> Allow adjustment of http block device's readahead size, via the
>>> environment variable "HTTP_READAHEAD_SIZE".
>>>
>>> Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
>>>
>>
>> I'd rather a command line option than an environmental variable.
>
> Wouldn't it make sense to pass arbitrary options via -drive to backends?
>
> That way we could have -drive 
> file=http://sample.com/test.iso,http-readahead=1024.

Where it gets complex is that you probably want those options to be 
included as qcow2 backing_file too.  I've thought about this in the past 
and haven't been able to come to a great solution.

Regards,

Anthony Liguori

> Alex
>

Re: [Qemu-devel] [PATCH] Allow adjustment of http block device's readahead size.

[Jamie Lokier]

Anthony Liguori wrote:
> Alexander Graf wrote:
> >
> >On 29.06.2009, at 15:45, Anthony Liguori wrote:
> >
> >>Nolan wrote:
> >>>Allow adjustment of http block device's readahead size, via the
> >>>environment variable "HTTP_READAHEAD_SIZE".
> >>>
> >>>Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
> >>>
> >>
> >>I'd rather a command line option than an environmental variable.
> >
> >Wouldn't it make sense to pass arbitrary options via -drive to backends?
> >
> >That way we could have -drive 
> >file=http://sample.com/test.iso,http-readahead=1024.
> 
> Where it gets complex is that you probably want those options to be 
> included as qcow2 backing_file too.  I've thought about this in the past 
> and haven't been able to come to a great solution.

And sometimes you want to change or override the qcow2 backing_file options...

It's already awkward when you want to rename a bunch of image files,
that the backing relative file path is fixed in the qcow2 file and
cannot be overridden by a management program (without rewriting the
qcow2 file).

Options like http-readahead=1024 on the backing file are the sort of
thing it's reasonable to want to change more often.  Imho they are in
the same category as the cache= option, which should be controllable
for backing files when invoking QEMU independently from the main file.

-- Jamie