[PATCH libdrm v3 2/5] xf86drm: Add USB support

[Thierry Reding]

Adding back dri-devel at lists.freedesktop.org

On Wed, Jan 18, 2017 at 12:21:23PM +0100, walter harms wrote:
> 
> 
> Am 18.01.2017 10:02, schrieb Thierry Reding:
> > Allow DRM/KMS devices hosted on USB to be detected by the drmDevice
> > infrastructure.
> > 
> > v3:
> > - guard Linux-specific sysfs parsing code with #ifdef __linux__
> > 
> > v2:
> > - make sysfs_uevent_get() more flexible using a format string
> > 
> > Signed-off-by: Thierry Reding <thierry.reding at gmail.com>
> > ---
> >  xf86drm.c | 175 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  xf86drm.h |  13 +++++
> >  2 files changed, 188 insertions(+)
> > 
> > diff --git a/xf86drm.c b/xf86drm.c
> > index 7766bfe937db..d83674e638c4 100644
> > --- a/xf86drm.c
> > +++ b/xf86drm.c
> > @@ -2886,6 +2886,50 @@ char *drmGetRenderDeviceNameFromFd(int fd)
> >      return drmGetMinorNameForFD(fd, DRM_NODE_RENDER);
> >  }
> >  
> > +#ifdef __linux__
> > +static char * DRM_PRINTFLIKE(2, 3)
> > +sysfs_uevent_get(const char *path, const char *fmt, ...)
> > +{
> > +    char filename[PATH_MAX + 1], *key, *line = NULL, *value = NULL;
>        char *filename=NULL, *key, *line = NULL, *value = NULL;
> > +    size_t size = 0, len;
> > +    ssize_t num;
> > +    va_list ap;
> > +    FILE *fp;
> > +
> > +    va_start(ap, fmt);
> > +    num = vasprintf(&key, fmt, ap);
> > +    va_end(ap);
> > +    len = num;
> > +
> > +    snprintf(filename, sizeof(filename), "%s/uevent", path);
> 
> 	since asprintf() is available you could use:
> 
>         asprintf(&filename,"%s/uevent", path);
> 
> 	same could be done for path below.

I had thought about that, but a stack-allocated string seemed
advantageous for three reasons:

	- asprintf() is a GNU extension. That's not much of an issue
	  because this is already protected by #ifdef __linux__ and
	  pretty much all C libraries I know support asprintf() and
	  friends.

	- PATH_MAX is the maximum length of a filename, so there's no
	  need to dynamically allocate, since it should nicely fit into
	  the stack pretty much everywhere (I think the largest value I
	  have ever seen for PATH_MAX is 4096 on recent Linux systems).

	- Most of the other code in xf86drm.c already uses PATH_MAX, so
	  the code remains consistent.

Given the added complexity of asprintf() and the need to free the memory
the advantages of the stack-allocated string seemed to outweigh.

Thierry
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