Re: [Qemu-block] [Qemu-devel] Patch to add helpful tracing output for driver authors in NVMe emulation

[Eric Blake]

On 10/05/2017 06:18 PM, Doug Gale wrote:
> I added the tracing output in this patch to assist me in implementing
> an NVMe driver. It helped tremendously.
> 
>>From 1d19086cdef8d492929852d582cb41dcc5026f71 Mon Sep 17 00:00:00 2001
> From: Doug Gale <address@hidden>
> Date: Thu, 5 Oct 2017 19:02:03 -0400
> Subject: [PATCH] Add tracing output to NVMe emulation to help driver authors.
> 
> It is off by default, enable it by uncommenting #define DEBUG_NVME
> or through CFLAGS
> 
> Signed-off-by: Doug Gale <address@hidden>
> ---
>  hw/block/nvme.c | 191 
> +++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 177 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index 9aa32692a3..74220c0171 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -36,6 +36,14 @@
> 
>  #include "nvme.h"
> 
> +//#define DEBUG_NVME
> +
> +#ifdef DEBUG_NVME
> +#define DPRINTF(fmt, ...) fprintf(stderr, "nvme: " fmt "\n", ## __VA_ARGS__)
> +#else
> +#define DPRINTF(fmt, ...) ((void)0)
> +#endif

As Kevin said, using trace-events is nicer than fprintf().  But if you
absolutely insist on fprintf(), then do NOT do it like this, because
this leads to bit-rot.  Instead, do it in a form that lets -Wformat
checking work even when tracing is disabled:

#ifdef DEBUG_NVME
# define DEBUG_NVME_PRINT 1
#else
# define DEBUG_NVME_PRINT 0
#endif
#define DPRINTF(fmt, ...) \
    do { \
        if (DEBUG_NVME_PRINT) { \
            fprintf(stderr, "nvme: " fmt "\n", ## __VA_ARGS__); \
        } \
    while (0)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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