[FFmpeg-devel] Patch for IPC SHM

[Aran.Clauson at wwu.edu]

From: Chad Fraleigh <chadf at triularity.org>
>
> On 7/22/2019 11:14 AM, Aran.Clauson at wwu.edu wrote:
>
>> +static void rm_shmid(AVFormatContext *s) {
>> +    XCBGrabContext *c = s->priv_data;
>> +    if(c->shmid != -1) {
>> +      shmctl(c->shmid, IPC_RMID, 0);
>> +      c->shmid == -1;
>          ^^^^^^^^^^^^^^
>   Assignment/compare operator mismatch.
>
>
>> +    }
>> +}
>> +

Well, that's embarrassing.

diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
index b7e689343e..1acf3cdf28 100644
--- a/libavdevice/xcbgrab.c
+++ b/libavdevice/xcbgrab.c
@@ -75,6 +75,7 @@ typedef struct XCBGrabContext {
     const char *framerate;

     int has_shm;
+    int shmid;
 } XCBGrabContext;

 #define FOLLOW_CENTER -1
@@ -221,6 +222,14 @@ static int check_shm(xcb_connection_t *conn)
     return 0;
 }

+static void rm_shmid(AVFormatContext *s) {
+    XCBGrabContext *c = s->priv_data;
+    if(c->shmid != -1) {
+      shmctl(c->shmid, IPC_RMID, 0);
+      c->shmid = -1;
+    }
+}
+
 static int allocate_shm(AVFormatContext *s)
 {
     XCBGrabContext *c = s->priv_data;
@@ -230,7 +239,8 @@ static int allocate_shm(AVFormatContext *s)

     if (c->buffer)
         return 0;
-    id = shmget(IPC_PRIVATE, size, IPC_CREAT | 0777);
+
+    id = shmget(IPC_PRIVATE, size, IPC_CREAT | 0666);
     if (id == -1) {
         char errbuf[1024];
         int err = AVERROR(errno);
@@ -239,15 +249,20 @@ static int allocate_shm(AVFormatContext *s)
                size, errbuf);
         return err;
     }
+
     xcb_shm_attach(c->conn, c->segment, id, 0);
     data = shmat(id, NULL, 0);
-    shmctl(id, IPC_RMID, 0);
-    if ((intptr_t)data == -1 || !data)
-        return AVERROR(errno);
+
+    if ((intptr_t)data == -1 || !data) {
+      shmctl(id, IPC_RMID, 0);
+      return AVERROR(errno);
+    }
     c->buffer = data;
+    c->shmid = id;
     return 0;
 }

+
 static int xcbgrab_frame_shm(AVFormatContext *s, AVPacket *pkt)
 {
     XCBGrabContext *c = s->priv_data;
@@ -268,6 +283,8 @@ static int xcbgrab_frame_shm(AVFormatContext *s, AVPacket *pkt)

     xcb_flush(c->conn);

+    rm_shmid(s);
+
     if (e) {
         av_log(s, AV_LOG_ERROR,
                "Cannot get the image data "


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