[pulseaudio-discuss] [PATCH 2/2] memblock: Avoid block ID collisions when exporting memory blocks

[David Henningsson]

Every new memexport object now gets an ever increasing base index,
that prevents block ID collisions between different memexport
objects on the same pstream.

In particular, this prevents block ID collision between the srb memblock
(which has its own memexport object) and audio data blocks.

Reported-by: Peter Meerwald <pmeerw at pmeerw.net>
Signed-off-by: David Henningsson <david.henningsson at canonical.com>
---
 src/pulsecore/memblock.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/pulsecore/memblock.c b/src/pulsecore/memblock.c
index ca24dec..2be0415 100644
--- a/src/pulsecore/memblock.c
+++ b/src/pulsecore/memblock.c
@@ -132,6 +132,7 @@ struct pa_memexport {
     PA_LLIST_HEAD(struct memexport_slot, free_slots);
     PA_LLIST_HEAD(struct memexport_slot, used_slots);
     unsigned n_init;
+    unsigned baseidx;
 
     /* Called whenever a client from which we imported a memory block
        which we in turn exported to another client dies and we need to
@@ -150,6 +151,7 @@ struct pa_mempool {
     size_t block_size;
     unsigned n_blocks;
     bool is_remote_writable;
+    unsigned export_baseidx;
 
     pa_atomic_t n_init;
 
@@ -1108,7 +1110,11 @@ pa_memexport* pa_memexport_new(pa_mempool *p, pa_memexport_revoke_cb_t cb, void
     e->userdata = userdata;
 
     pa_mutex_lock(p->mutex);
+
     PA_LLIST_PREPEND(pa_memexport, p->exports, e);
+    e->baseidx = p->export_baseidx;
+    p->export_baseidx += PA_MEMEXPORT_SLOTS_MAX;
+
     pa_mutex_unlock(p->mutex);
     return e;
 }
@@ -1118,7 +1124,7 @@ void pa_memexport_free(pa_memexport *e) {
 
     pa_mutex_lock(e->mutex);
     while (e->used_slots)
-        pa_memexport_process_release(e, (uint32_t) (e->used_slots - e->slots));
+        pa_memexport_process_release(e, (uint32_t) (e->used_slots - e->slots + e->baseidx));
     pa_mutex_unlock(e->mutex);
 
     pa_mutex_lock(e->pool->mutex);
@@ -1137,6 +1143,10 @@ int pa_memexport_process_release(pa_memexport *e, uint32_t id) {
 
     pa_mutex_lock(e->mutex);
 
+    if (id < e->baseidx)
+        goto fail;
+    id -= e->baseidx;
+
     if (id >= e->n_init)
         goto fail;
 
@@ -1185,7 +1195,7 @@ static void memexport_revoke_blocks(pa_memexport *e, pa_memimport *i) {
             slot->block->per_type.imported.segment->import != i)
             continue;
 
-        idx = (uint32_t) (slot - e->slots);
+        idx = (uint32_t) (slot - e->slots + e->baseidx);
         e->revoke_cb(e, idx, e->userdata);
         pa_memexport_process_release(e, idx);
     }
@@ -1246,7 +1256,7 @@ int pa_memexport_put(pa_memexport *e, pa_memblock *b, uint32_t *block_id, uint32
 
     PA_LLIST_PREPEND(struct memexport_slot, e->used_slots, slot);
     slot->block = b;
-    *block_id = (uint32_t) (slot - e->slots);
+    *block_id = (uint32_t) (slot - e->slots + e->baseidx);
 
     pa_mutex_unlock(e->mutex);
 /*     pa_log("Got block id %u", *block_id); */
-- 
1.9.1