Re: [Qemu-devel] [PATCH] qtest: ask endianness of the target in qtest_init()

[Greg Kurz <groug@kaod.org>]

On Fri, 7 Oct 2016 09:10:14 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> On 06/10/2016 22:45, Peter Maydell wrote:
> > On 6 October 2016 at 11:56, Laurent Vivier <lvivier@redhat.com> wrote:  
> >> The target endianness is not deduced anymore from
> >> the architecture name but asked directly to the guest,
> >> using a new qtest command: "endianness". As it can't
> >> change (this is the value of TARGET_WORDS_BIGENDIAN),
> >> we store it to not have to ask every time we want to
> >> know if we have to byte-swap a value.
> >>
> >> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> >> CC: Greg Kurz <groug@kaod.org>
> >> CC: David Gibson <david@gibson.dropbear.id.au>
> >> CC: Peter Maydell <peter.maydell@linaro.org>
> >> ---
> >> Note: this patch can be seen as a v2 of
> >> "qtest: evaluate endianness of the target in qtest_init()"
> >> from the patch series "tests: enable virtio tests on SPAPR"
> >> in which I have added the idea from Peter to ask the endianness
> >> directly to the guest using a new qtest command.
> >>
> >>  qtest.c                   |   7 ++
> >>  tests/libqos/virtio-pci.c |   2 +-
> >>  tests/libqtest.c          | 224 ++++++++++++++++++++--------------------------
> >>  tests/libqtest.h          |  16 +++-
> >>  tests/virtio-blk-test.c   |   2 +-
> >>  5 files changed, 118 insertions(+), 133 deletions(-)
> >>
> >> diff --git a/qtest.c b/qtest.c
> >> index 22482cc..b53b39c 100644
> >> --- a/qtest.c
> >> +++ b/qtest.c
> >> @@ -537,6 +537,13 @@ static void qtest_process_command(CharDriverState *chr, gchar **words)
> >>
> >>          qtest_send_prefix(chr);
> >>          qtest_send(chr, "OK\n");
> >> +    } else if (strcmp(words[0], "endianness") == 0) {
> >> +        qtest_send_prefix(chr);
> >> +#if defined(TARGET_WORDS_BIGENDIAN)
> >> +        qtest_sendf(chr, "OK big\n");
> >> +#else
> >> +        qtest_sendf(chr, "OK little\n");
> >> +#endif
> >>  #ifdef TARGET_PPC64
> >>      } else if (strcmp(words[0], "rtas") == 0) {
> >>          uint64_t res, args, ret;
> >> diff --git a/tests/libqos/virtio-pci.c b/tests/libqos/virtio-pci.c
> >> index 18b92b9..6e005c1 100644
> >> --- a/tests/libqos/virtio-pci.c
> >> +++ b/tests/libqos/virtio-pci.c
> >> @@ -86,7 +86,7 @@ static uint64_t qvirtio_pci_config_readq(QVirtioDevice *d, uint64_t addr)
> >>      int i;
> >>      uint64_t u64 = 0;
> >>
> >> -    if (qtest_big_endian()) {
> >> +    if (target_big_endian()) {
> >>          for (i = 0; i < 8; ++i) {
> >>              u64 |= (uint64_t)qpci_io_readb(dev->pdev,
> >>                                  (void *)(uintptr_t)addr + i) << (7 - i) * 8;  
> > 
> > Why rename the function? We're only changing its
> > implementation.  
> 
> Because in libqtest.c, qtest_XXXX() functions take always a QTestState
> argument, and then in libqtest.h, we have an inline like "inline static
> XXXX(...) { qtest_XXXX(global_qtest ...) }".
> 
> >> diff --git a/tests/libqtest.c b/tests/libqtest.c
> >> index 6f6bdf1..27cf6b1 100644
> >> --- a/tests/libqtest.c
> >> +++ b/tests/libqtest.c
> >> @@ -37,6 +37,7 @@ struct QTestState
> >>      bool irq_level[MAX_IRQ];
> >>      GString *rx;
> >>      pid_t qemu_pid;  /* our child QEMU process */
> >> +    bool big_endian;
> >>  };
> >>
> >>  static GHookList abrt_hooks;
> >> @@ -146,89 +147,6 @@ void qtest_add_abrt_handler(GHookFunc fn, const void *data)
> >>      g_hook_prepend(&abrt_hooks, hook);
> >>  }
> >>
> >> -QTestState *qtest_init(const char *extra_args)
> >> -{
> >> -    QTestState *s;
> >> -    int sock, qmpsock, i;
> >> -    gchar *socket_path;
> >> -    gchar *qmp_socket_path;
> >> -    gchar *command;
> >> -    const char *qemu_binary;
> >> -
> >> -    qemu_binary = getenv("QTEST_QEMU_BINARY");
> >> -    g_assert(qemu_binary != NULL);  
> > 
> > This diff arrangement makes the patch a bit hard to read;
> > what meant that the functions had to be moved around?  
> 
> Yes, I know. I move this function after qtest_sendf() and qtest_rsp() to
> not have to declare them before. There are no circular dependencies, so
> we can.
> 
> >   
> >> +    /* ask endianness of the target */
> >> +
> >> +    qtest_sendf(s, "endianness\n");
> >> +    args = qtest_rsp(s, 1);
> >> +    g_assert(strcmp(args[1], "big") == 0 || strcmp(args[1], "little") == 0);
> >> +    s->big_endian = strcmp(args[1], "big") == 0;
> >> +    g_strfreev(args);  
> > 
> > This would be better in its own utility function, I think.  
> 
> Yes, I agree, but my wondering was how to name it :P ,
> qtest_big_endian() and target_big_endian() are already in use, and as it
> is a 6 lines function, used once, I guessed we could inline it here.
> 

This is TARGET_WORDS_BIGENDIAN which is constant for a single QEMU
run... why moving it to a function ? Unless there are plans to
have dynamic target endianness in QEMU, I guess it makes more
sense to open code as you did.

Cheers.

--
Greg

> Thanks,
> Laurent