Add support for the named shared memory to the proxy library

Add support for the named shared memory to the proxy library.
It adds the UMF_PROXY="page.disposition=shared-shm"
environment variable for the MAP_SHARED visibility mode
with the named shared memory using a generated SHM name.

Signed-off-by: Lukasz Dorau <[email protected]>

Author: ldorau

README.md

@@ -256,7 +256,9 @@ $ LD_PRELOAD=/usr/lib/libumf_proxy.so myprogram
 
 The memory used by the proxy memory allocator is mmap'ed:
 1) with the `MAP_PRIVATE` flag by default or
-2) with the `MAP_SHARED` flag only if the `UMF_PROXY` environment variable contains the `page.disposition=shared` string.
+2) with the `MAP_SHARED` flag if the `UMF_PROXY` environment variable contains one of two following strings: `page.disposition=shared-shm` or `page.disposition=shared-fd`. These two options differ in a mechanism used during IPC:
+   - `page.disposition=shared-shm` - IPC uses the named shared memory. An SHM name is generated using the `umf_proxy_lib_shm_pid_$PID` pattern, where `$PID` is the PID of the process. It creates the `/dev/shm/umf_proxy_lib_shm_pid_$PID` file.
+   - `page.disposition=shared-fd` - IPC uses the file descriptor duplication. It requires using `pidfd_getfd(2)` to obtain a duplicate of another process's file descriptor. Permission to duplicate another process's file descriptor is governed by a ptrace access mode `PTRACE_MODE_ATTACH_REALCREDS` check (see `ptrace(2)`) that can be changed using the `/proc/sys/kernel/yama/ptrace_scope` interface. `pidfd_getfd(2)` is supported since Linux 5.6.
 
 #### Windows
 

src/proxy_lib/proxy_lib.c

@@ -112,10 +112,30 @@ void proxy_lib_create_common(void) {
     umf_result_t umf_result;
 
 #ifndef _WIN32
-    if (util_env_var_has_str("UMF_PROXY", "page.disposition=shared")) {
-        LOG_DEBUG("proxy_lib: using the MAP_SHARED visibility mode");
+#define NAME_MAX 255
+    char shm_name[NAME_MAX];
+
+    if (util_env_var_has_str("UMF_PROXY", "page.disposition=shared-fd")) {
+        LOG_DEBUG("proxy_lib: using the MAP_SHARED visibility mode with the "
+                  "file descriptor duplication");
+        os_params.visibility = UMF_MEM_MAP_SHARED;
+        os_params.shm_name = NULL;
+
+    } else if (util_env_var_has_str("UMF_PROXY",
+                                    "page.disposition=shared-shm")) {
+        LOG_DEBUG("proxy_lib: using the MAP_SHARED visibility mode with the "
+                  "named shared memory");
         os_params.visibility = UMF_MEM_MAP_SHARED;
+
+        memset(shm_name, 0, NAME_MAX);
+        sprintf(shm_name, "umf_proxy_lib_shm_pid_%i", utils_getpid());
+        os_params.shm_name = shm_name;
+
+        LOG_DEBUG("proxy_lib: using the MAP_SHARED visibility mode with the "
+                  "named shared memory: %s",
+                  os_params.shm_name);
     }
+#undef NAME_MAX
 #endif
 
     umf_result = umfMemoryProviderCreate(umfOsMemoryProviderOps(), &os_params,