Re: [Qemu-devel] [PATCH] qemu-io: add option to enable tracing

[Kevin Wolf <kwolf@redhat.com>]

Am 12.03.2012 12:39, schrieb Stefan Hajnoczi:
> On Wed, Dec 21, 2011 at 3:35 PM, Stefan Hajnoczi
> <stefanha@linux.vnet.ibm.com> wrote:
> 
> Ping?  Do you want to take this through the block tree?

Sorry, I completely missed this one.

>> It can be useful to enable QEMU tracing when trying out block layer
>> interfaces via qemu-io.  Tracing can be enabled using the new -t FILE
>> option where the given file contains a list of trace events to enable
>> (just like the qemu --trace events=FILE option).
>>
>>  $ echo qemu_vfree >my-events
>>  $ ./qemu-io -t my-events ...
>>
>> Remember to use ./configure --enable-trace-backend=BACKEND when building
>> qemu-io.
>>
>> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
>> ---
>>  qemu-io.c |    8 +++++++-
>>  1 files changed, 7 insertions(+), 1 deletions(-)
>>
>> diff --git a/qemu-io.c b/qemu-io.c
>> index ffa62fb..ad91fd6 100644
>> --- a/qemu-io.c
>> +++ b/qemu-io.c
>> @@ -17,6 +17,7 @@
>>  #include "qemu-common.h"
>>  #include "block_int.h"
>>  #include "cmd.h"
>> +#include "trace/control.h"
>>
>>  #define VERSION        "0.0.1"
>>
>> @@ -1722,6 +1723,7 @@ static void usage(const char *name)
>>  "  -g, --growable       allow file to grow (only applies to protocols)\n"
>>  "  -m, --misalign       misalign allocations for O_DIRECT\n"
>>  "  -k, --native-aio     use kernel AIO implementation (on Linux only)\n"
>> +"  -t, --trace FILE     enable trace events listed in the given file\n"
>>  "  -h, --help           display this help and exit\n"
>>  "  -V, --version        output version information and exit\n"
>>  "\n",
>> @@ -1733,7 +1735,7 @@ int main(int argc, char **argv)
>>  {
>>     int readonly = 0;
>>     int growable = 0;
>> -    const char *sopt = "hVc:rsnmgk";
>> +    const char *sopt = "hVc:rsnmgkt:";
>>     const struct option lopt[] = {
>>         { "help", 0, NULL, 'h' },
>>         { "version", 0, NULL, 'V' },
>> @@ -1745,6 +1747,7 @@ int main(int argc, char **argv)
>>         { "misalign", 0, NULL, 'm' },
>>         { "growable", 0, NULL, 'g' },
>>         { "native-aio", 0, NULL, 'k' },
>> +        { "trace", 1, NULL, 't' },
>>         { NULL, 0, NULL, 0 }
>>     };
>>     int c;
>> @@ -1776,6 +1779,9 @@ int main(int argc, char **argv)
>>         case 'k':
>>             flags |= BDRV_O_NATIVE_AIO;
>>             break;
>> +        case 't':
>> +            trace_backend_init(optarg, NULL);
>> +            break;

vl.c checks the return value of trace_backend_init. Shouldn't we do the
same here?

Also, I was considering adding a -t for the cache mode (option name for
consistency with qemu-img). Conversely, we'll probably want to add a
tracing option to qemu-img and -t isn't available any more there. Maybe
we should use a different letter?

Kevin