libc+init+shmem-test: Add POSIX shared memory objects

apps/init.cpp

@@ -292,6 +292,15 @@ static void mount_tmpfs()
     if (chmod("/tmp", 01777) < 0) exit(255);
 }
 
+static void mount_shmfs()
+{
+    if (mkdir("/dev/shm", 0755) < 0) exit(255);
+
+    if (mount("/dev/shm", "tmpfs", "tmpfs") < 0) exit(255);
+
+    if (chmod("/dev/shm", 01777) < 0) exit(255);
+}
+
 int main()
 {
     if (getpid() != 1)
@@ -307,6 +316,7 @@ int main()
     stderr = fopen("/dev/console", "w");
 
     mount_tmpfs();
+    mount_shmfs();
 
     umask(022);
 

apps/shmem-test.cpp

@@ -1,3 +1,4 @@
+#include <fcntl.h>
 #include <stdio.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
@@ -5,15 +6,27 @@
 
 int main()
 {
-    void* address = mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+    int fd = shm_open("/shared", O_CREAT | O_RDWR, 0666);
+    if (fd < 0)
+    {
+        perror("shm_open");
+        return 1;
+    }
+
+    ftruncate(fd, PAGE_SIZE);
+
+    void* address = mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
     if (address == MAP_FAILED)
     {
         perror("mmap");
         return 1;
     }
 
-    int* ptr = (int*)address;
-    *ptr = 16;
+    char* ptr = (char*)address;
+
+    printf("the value is %c\n", *ptr);
+
+    *ptr = 'a';
 
     pid_t child = fork();
     if (child < 0)
@@ -23,13 +36,13 @@ int main()
     }
     if (child == 0)
     {
-        *ptr = 32;
+        *ptr = 'e';
         _exit(0);
     }
 
     waitpid(child, NULL, 0);
 
-    printf("the value is %d\n", *ptr);
+    printf("the value is %c\n", *ptr);
 
     return 0;
 }

libc/include/sys/mman.h

@@ -28,6 +28,12 @@ extern "C"
     /* Write modified shared memory back to its associated file. */
     int msync(void* addr, size_t len, int flags);
 
+    /* Create a new POSIX shared memory object. */
+    int shm_open(const char* name, int oflag, mode_t mode);
+
+    /* Delete a POSIX shared memory object from the file system. */
+    int shm_unlink(const char* name);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/sys/mman.cpp

@@ -1,6 +1,8 @@
 #include <bits/errno-return.h>
 #include <bits/mmap.h>
+#include <fcntl.h>
 #include <luna/Heap.h>
+#include <stdio.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
@@ -25,4 +27,18 @@ extern "C"
         long rc = syscall(SYS_msync, addr, len);
         __errno_return(rc, int);
     }
+
+    int shm_open(const char* name, int oflag, mode_t mode)
+    {
+        char buf[BUFSIZ];
+        snprintf(buf, sizeof(buf), "/dev/shm%s", name);
+        return open(buf, oflag | O_CLOEXEC, mode);
+    }
+
+    int shm_unlink(const char* name)
+    {
+        char buf[BUFSIZ];
+        snprintf(buf, sizeof(buf), "/dev/shm%s", name);
+        return unlink(buf);
+    }
 }