util: Introduce the shmalloc helper

This one allocates a memory, that will be shared (MAP_SHARED)
between all the subsequent children. This can now be just used
for fd resote, later it will be required at inet socket port
binding.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

files.c

@@ -27,9 +27,6 @@
 #include "protobuf.h"
 #include "protobuf/fs.pb-c.h"
 
-static struct fdinfo_list_entry *fdinfo_list;
-static int nr_fdinfo_list;
-
 #define FDESC_HASH_SIZE	64
 static struct list_head file_desc_hash[FDESC_HASH_SIZE];
 
@@ -39,13 +36,6 @@ int prepare_shared_fdinfo(void)
 {
 	int i;
 
-	fdinfo_list = mmap(NULL, FDINFO_POOL_SIZE,
-			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, 0, 0);
-	if (fdinfo_list == MAP_FAILED) {
-		pr_perror("Can't map fdinfo_list");
-		return -1;
-	}
-
 	for (i = 0; i < FDESC_HASH_SIZE; i++)
 		INIT_LIST_HEAD(&file_desc_hash[i]);
 
@@ -161,17 +151,15 @@ int rst_file_params(int fd, FownEntry *fown, int flags)
 
 static int collect_fd(int pid, FdinfoEntry *e, struct rst_info *rst_info)
 {
-	struct fdinfo_list_entry *l, *le = &fdinfo_list[nr_fdinfo_list];
+	struct fdinfo_list_entry *l, *le;
 	struct file_desc *fdesc;
 
 	pr_info("Collect fdinfo pid=%d fd=%d id=0x%16x\n",
 		pid, e->fd, e->id);
 
-	nr_fdinfo_list++;
-	if ((nr_fdinfo_list) * sizeof(struct fdinfo_list_entry) >= FDINFO_POOL_SIZE) {
-		pr_err("OOM storing fdinfo_list_entries\n");
+	le = shmalloc(sizeof(*le));
+	if (!le)
 		return -1;
-	}
 
 	le->pid = pid;
 	futex_init(&le->real_pid);

include/util.h

@@ -318,4 +318,6 @@ static inline int read_img_str(int fd, char **pstr, int size)
 	return 0;
 }
 
+extern void *shmalloc(size_t bytes);
+
 #endif /* UTIL_H_ */

util.c

@@ -294,3 +294,34 @@ int is_anon_link_type(int lfd, char *type)
 	snprintf(aux, sizeof(aux), "anon_inode:%s", type);
 	return !strcmp(link, aux);
 }
+
+static void *sh_buf;
+static unsigned int sh_bytes_left;
+#define SH_BUF_CHUNK	4096
+
+void *shmalloc(size_t bytes)
+{
+	void *ret;
+
+	if (bytes > SH_BUF_CHUNK) {
+		pr_err("Too big shared buffer requested %lu\n", bytes);
+		return NULL;
+	}
+
+	if (sh_bytes_left < bytes) {
+		sh_buf = mmap(NULL, SH_BUF_CHUNK, PROT_READ | PROT_WRITE,
+				MAP_SHARED | MAP_ANON, 0, 0);
+		if (sh_buf == MAP_FAILED) {
+			pr_perror("Can't alloc shared buffer");
+			return NULL;
+		}
+
+		sh_bytes_left = SH_BUF_CHUNK;
+	}
+
+	ret = sh_buf;
+	sh_buf += bytes;
+	sh_bytes_left -= bytes;
+
+	return ret;
+}