[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_z

From: Peter Lieven
Subject: Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes
Date: Wed, 07 May 2014 18:02:52 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

On 07.05.2014 17:45, Peter Lieven wrote:
On 07.05.2014 17:38, Kevin Wolf wrote:
Am 07.05.2014 um 17:26 hat Peter Lieven geschrieben:
On 07.05.2014 17:19, Kevin Wolf wrote:
Am 07.05.2014 um 16:26 hat Peter Lieven geschrieben:
On 07.05.2014 04:52, Eric Blake wrote:
On 05/06/2014 06:23 PM, Peter Lieven wrote:
this patch tries to optimize zero write requests
by automatically using bdrv_write_zeroes if it is
supported by the format.

This significantly speeds up file system initialization and
should speed zero write test used to test backend storage

Signed-off-by: Peter Lieven <address@hidden>
v2->v3: - moved parameter parsing to blockdev_init
         - added per device detect_zeroes status to
           hmp (info block -v) and qmp (query-block) [Eric]
         - added support to enable detect-zeroes also
           for hot added devices [Eric]
         - added missing entry to qemu_common_drive_opts
         - fixed description of qemu_iovec_is_zero [Fam]

+static BdrvDetectZeroes parse_detect_zeroes(const char *buf, Error **errp)
+    if (!buf || !strcmp(buf, "off")) {
+        return BDRV_DETECT_ZEROES_OFF;
+    } else if (!strcmp(buf, "on")) {
+        return BDRV_DETECT_ZEROES_ON;
+    } else if (!strcmp(buf, "unmap")) {
+    } else {
+        error_setg(errp, "invalid value for detect-zeroes: %s",
+                   buf);
+    }
Isn't there QAPI generated code that you can use instead of open-coding
this conversion between string and enum values?
Actually I have no idea. As you pointed out in the qapi patch I sent
it was quite hard for me to crawl through the whole stuff as one who is not
familiar with it. Can somebody advise here? Anyhow, I wonder
how this would work since qapi doesn't know the C Macros.
QAPI does generate C enums, so you should take whatever identifier it
uses instead of defining your own macros. You may need to include
qapi-types.h for this. It also creates a *_lookup array that maps enum
IDs to strings.
Ah, cool stuff, thank you. I found the enum and the lookup array,
but is there also a function that maps a string to an enum ID?
I don't think so, but if you need it, you're probably doing something
wrong because QAPI already calls you with an enum parameter and not a
char* one.
I am in blockdev_init and want to set dinfo->bdrv->detect_zeroes to
the correct ID. Do you have a fast solution? Everything else in this
function is not using QAPI calls.

Actually, there is already a manual parsing for the werror and rerror in this 

I think for the future there might be need for a generic function that maps a 
to the ID of an enum object.

If you don't have objections I would leave the parsing function as is for the 


reply via email to

[Prev in Thread] Current Thread [Next in Thread]