[Mesa-dev] [PATCH] egl/drm: Try to use CLOEXEC for drm fds

[Derek Foreman]

On 12/06/15 11:29 AM, Emil Velikov wrote:
> Hi Derek,

Hi, thanks for looking at this. :)

> On 1 May 2015 at 18:34, Derek Foreman <derekf at osg.samsung.com> wrote:
>> These fds can propagate to child processes if we don't set CLOEXEC,
>> so make a best effort to do that.
>>
>> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
>> ---
>> Noticed this when fixing up similar problems in weston - weston's
>> drm fd gets dup()ed here and loses CLOEXEC and ends up in every child
>> process the shell launches.
>>
>>  src/egl/drivers/dri2/platform_drm.c | 14 +++++++++++---
>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c
>> index 486b003..c326d6c 100644
>> --- a/src/egl/drivers/dri2/platform_drm.c
>> +++ b/src/egl/drivers/dri2/platform_drm.c
>> @@ -596,7 +596,11 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
>>     struct dri2_egl_display *dri2_dpy;
>>     struct gbm_device *gbm;
>>     int fd = -1;
>> -   int i;
>> +   int i, flags = O_RDWR;
>> +
>> +#ifdef O_CLOEXEC
>> +   flags |= O_CLOEXEC;
>> +#endif
>>
>>     loader_set_logger(_eglLog);
>>
>> @@ -611,9 +615,9 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
>>        char buf[64];
>>        int n = snprintf(buf, sizeof(buf), DRM_DEV_NAME, DRM_DIR_NAME, 0);
>>        if (n != -1 && n < sizeof(buf))
>> -         fd = open(buf, O_RDWR);
>> +         fd = open(buf, flags);
>>        if (fd < 0)
>> -         fd = open("/dev/dri/card0", O_RDWR);
>> +         fd = open("/dev/dri/card0", flags);
>>        dri2_dpy->own_device = 1;
>>        gbm = gbm_create_device(fd);
>>        if (gbm == NULL)
>> @@ -639,6 +643,10 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
>>        }
>>     }
>>
>> +   flags = fcntl(dri2_dpy->fd, F_GETFD);
>> +   if (flags >= 0 && !(flags & FD_CLOEXEC))
>> +      fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
>> +
> In other places in mesa we explicitly check for EINVAL if open()
> fails, and use that as indication that O_CLOEXEC is not supported
> (note that we only use the O_RDWR and O_CLOEXEC flags). Curious which
> would be the better approach to use through mesa ?

Oops - I think that way is better.

There's a simple function in loader.c called drm_open_device() that does
the open that way, could we just rename that to loader_open_device() and
make it non-static and call it from dri2_initialize_drm()?

That said...

Unfortunately, it appears my previous testing was insufficient and
there's still a leaked fd - dup() creates fds without CLOEXEC set.

I've sent another couple of patches to this effect...