userspace/libwr: new shmem, split per-process and w/ bigger size

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

userspace/libwr/include/libwr/shmem.h

@@ -6,10 +6,11 @@
 #define __WRS_SHM_H__
 #include <stdint.h>
 
-#define WRS_SHM_FILE  "/dev/shm/wrs-shmem"
-#define WRS_SHM_SIZE  (64*1024) /* each */
+#define WRS_SHM_FILE  "/dev/shm/wrs-shmem-%i"
+#define WRS_SHM_MIN_SIZE    (4*1024)
+#define WRS_SHM_MAX_SIZE  (256*1024)
 
-/* Every process gets 8 pages (32k) to be safe for the future */
+/* Each process "name" (i.e. id) is added to the filename above */
 enum wrs_shm_name {
 	wrs_shm_ptp,
 	wrs_shm_rtu,
@@ -25,7 +26,7 @@ struct wrs_shm_head {
 
 	unsigned long stamp;	/* Last modified, w/ CLOCK_MONOTONIC */
 	unsigned long data_off;	/* Where the structure lives */
-	int shm_name;		/* The enum above, for cross-checking */
+	int fd;			/* So we can enlarge it using fd */
 	int pid;		/* The current pid owning the area */
 
 	unsigned pidsequence;	/* Each new pid must increments this */

userspace/libwr/shmem.c

 /* Alessandro Rubini for CERN 2014, LGPL-2.1 or later */
+#include <stdio.h>
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
@@ -18,6 +19,7 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
 	struct wrs_shm_head *head;
 	struct stat stbuf;
 	void *map;
+	char fname[64];
 	int write_access = flags & WRS_SHM_WRITE;
 	int fd;
 
@@ -26,20 +28,22 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
 		return NULL;
 	}
 
-	fd = open(WRS_SHM_FILE, O_RDWR | O_CREAT | O_SYNC, 0644);
+	sprintf(fname, WRS_SHM_FILE, name_id);
+	fd = open(fname, O_RDWR | O_CREAT | O_SYNC, 0644);
 	if (fd < 0)
 		return NULL; /* keep errno */
-	/* The file may be too short: enlarge it as needed */
+	/* The file may be too short: enlarge it to the minimum size */
+
 	if (fstat(fd, &stbuf) < 0)
 		return NULL; /* keep errno */
-	if (stbuf.st_size < WRS_SHM_SIZE * (name_id + 1)) {
-		lseek(fd, WRS_SHM_SIZE * (name_id + 1) -1, SEEK_SET);
+	if (stbuf.st_size < WRS_SHM_MIN_SIZE) {
+		lseek(fd, WRS_SHM_MIN_SIZE - 1, SEEK_SET);
 		write(fd, "", 1);
 	}
 
-	map = mmap(0, WRS_SHM_SIZE,
+	map = mmap(0, WRS_SHM_MAX_SIZE,
 		   PROT_READ | (write_access ? PROT_WRITE : 0),
-		   MAP_SHARED, fd, WRS_SHM_SIZE * name_id);
+		   MAP_SHARED, fd, 0);
 	if (map == MAP_FAILED)
 		return NULL; /* keep errno */
 	if (!write_access)
@@ -48,10 +52,11 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
 	/* Init the fields */
 	head = map;
 	if (head->pid && kill(head->pid, 0) == 0) {
-		munmap(map, WRS_SHM_SIZE);
+		munmap(map, WRS_SHM_MAX_SIZE);
 		errno = EBUSY;
 		return NULL;
 	}
+	head->fd = fd;
 	head->sequence = 1; /* a sort of lock */
 	head->mapbase = head;
 	strncpy(head->name, name, sizeof(head->name));
@@ -59,7 +64,6 @@ void *wrs_shm_get(enum wrs_shm_name name_id, char *name, unsigned long flags)
 	head->stamp = 0;
 	head->data_off = sizeof(*head);
 	head->data_size = 0;
-	head->shm_name = name_id;
 	head->pid = getpid();
 	head->pidsequence++;
 	/* version and size are up to the user (or to allocation) */
@@ -74,9 +78,11 @@ int wrs_shm_put(void *headptr)
 {
 	struct wrs_shm_head *head = headptr;
 	int err;
-	if (head->pid == getpid())
+	if (head->pid == getpid()) {
 		head->pid = 0; /* mark that we are not writers any more */
-	if ((err = munmap(headptr, WRS_SHM_SIZE)) < 0)
+		close(head->fd);
+	}
+	if ((err = munmap(headptr, WRS_SHM_MAX_SIZE)) < 0)
 		return err;
 	return 0;
 }
@@ -89,10 +95,15 @@ void *wrs_shm_alloc(void *headptr, size_t size)
 
 	if (head->pid != getpid())
 		return NULL; /* we are not writers */
-	if (head->data_off + head->data_size + size > WRS_SHM_SIZE)
+	if (head->data_off + head->data_size + size > WRS_SHM_MAX_SIZE)
 		return NULL; /* no space left */
 	nextptr = headptr + head->data_off + head->data_size;
 	head->data_size += (size + 7) & ~7; /* force 8-alignment */
+
+	/* Before we write to shmem, ensure the backing store exists */
+	lseek(head->fd, head->data_off + head->data_size - 1, SEEK_SET);
+	write(head->fd, "", 1);
+
 	memset(nextptr, 0, size);
 	return nextptr;
 }
@@ -102,7 +113,7 @@ void *wrs_shm_follow(void *headptr, void *ptr)
 {
 	struct wrs_shm_head *head = headptr;
 
-	if (ptr < head->mapbase || ptr > head->mapbase + WRS_SHM_SIZE)
+	if (ptr < head->mapbase || ptr > head->mapbase + WRS_SHM_MAX_SIZE)
 		return NULL; /* not in the area */
 	return headptr + (ptr - head->mapbase);
 }

ppsi @ f49685ec

-Subproject commit 52fda5e90fd10e42f867b8c21a5fd9e42fb2dbfd
+Subproject commit f49685ec07132da80b8aec32a2d50d143d23e13d