Switch from ioctl to dm target messages for PID blacklist/whitelist m…

…anipulation

In mainline 4.4 the ioctl() callback in the DM target has been removed
in favour of a prepare_ioctl() which selects the underlying device,
all ioctls are assume to apply to that.  In discussions with upstream on
resolving this it was suggested that the correct mechanism for this
kind of target focussed ioctl is actually DM target messages.  This
patch converts the blacklist/whitelist manipulation over to these DM
target messages.

It also adds rather primative support to the flashcache_setioctl helper to
switch to DM target messages when the existing ioctls are not supported
(ENOTTY).  This is handled by calling out to dmsetup which offers a
message command to form these requests.

I would envisage it would be possible to reduce flashcache_setioctl to a
simple shell script in the future once there is no possibility of these
tools being used with a kernel supporting the ioctl only.

This should fix the hard parts of issue facebookarchive#215.

fixes: facebookarchive#215
Signed-off-by: Andy Whitcroft <apw@ubuntu.com>

src/flashcache_conf.c

@@ -1713,7 +1713,12 @@ static struct target_type flashcache_target = {
 	.dtr    = flashcache_dtr,
 	.map    = flashcache_map,
 	.status = flashcache_status,
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4,4,0)
 	.ioctl 	= flashcache_ioctl,
+#else
+	.prepare_ioctl 	= flashcache_prepare_ioctl,
+	.message        = flashcache_message,
+#endif
 	.iterate_devices = flashcache_iterate_devices,
 };
 

src/flashcache_ioctl.c

@@ -503,6 +503,82 @@ skip_sequential_io(struct cache_c *dmc, struct bio *bio)
  * exit, for cases where the process dies after marking itself
  * non-cacheable.
  */
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,4,0)
+int
+flashcache_prepare_ioctl(struct dm_target *ti,
+			 struct block_device **bdev, fmode_t *mode)
+{
+	struct cache_c *dmc = (struct cache_c *) ti->private;
+
+	*bdev = dmc->disk_dev->bdev;
+
+	return 0;
+}
+
+int
+flashcache_message(struct dm_target *ti, unsigned argc, char **argv)
+{
+	struct cache_c *dmc = (struct cache_c *) ti->private;
+	int list;
+	long long upid;
+	pid_t pid = 0;
+
+	/*
+	 * whitelist|blacklist add|del <pid>
+	 * whitelist|blacklist delall
+	 */
+	if (argc < 2)
+		return -EINVAL;
+
+	/* Decode the primary command. */
+	if (strcmp(argv[0], "whitelist") == 0) {
+		list = FLASHCACHE_WHITELIST;
+	} else if (strcmp(argv[0], "blacklist") == 0) {
+		list = FLASHCACHE_BLACKLIST;
+	} else {
+		return -EINVAL;
+	}
+
+	/* Decode the sub-command. */
+	if (strcmp(argv[1], "add") == 0) {
+		int rr;
+		if (argc != 3)
+			return -EINVAL;
+
+		/* Decode the pid. */
+		if (kstrtoull(argv[2], 10, &upid))
+			return -EINVAL;
+		pid = (pid_t)upid;
+
+		flashcache_add_pid(dmc, pid, list);
+		return 0;
+
+	} else if (strcmp(argv[1], "del") == 0) {
+		if (argc != 3)
+			return -EINVAL;
+
+		/* Decode the pid. */
+		if (kstrtoull(argv[2], 10, &upid))
+			return -EINVAL;
+		pid = (pid_t)upid;
+
+		flashcache_del_pid(dmc, pid, list);
+		return 0;
+
+	} else if (strcmp(argv[1], "delall") == 0) {
+		if (argc != 2)
+			return -EINVAL;
+
+		flashcache_del_all_pids(dmc, list, 0);
+		return 0;
+
+	} else {
+		return -EINVAL;
+	}
+}
+
+#else
+
 int 
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,27)
 flashcache_ioctl(struct dm_target *ti, struct inode *inode,
@@ -561,3 +637,5 @@ flashcache_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
 	}
 
 }
+
+#endif

src/flashcache_ioctl.h

@@ -51,6 +51,11 @@ enum {
 #define FLASHCACHEDELALLWHITELIST	_IOW(FLASHCACHE_IOCTL, FLASHCACHEDELWHITELISTALL_CMD, pid_t)
 
 #ifdef __KERNEL__
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,4,0)
+int flashcache_message(struct dm_target *ti, unsigned argc, char **argv);
+int flashcache_prepare_ioctl(struct dm_target *ti,
+                             struct block_device **bdev, fmode_t *mode);
+#else
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,27)
 int flashcache_ioctl(struct dm_target *ti, struct inode *inode,
 		     struct file *filp, unsigned int cmd,
@@ -59,6 +64,7 @@ int flashcache_ioctl(struct dm_target *ti, struct inode *inode,
 int flashcache_ioctl(struct dm_target *ti, unsigned int cmd,
  		     unsigned long arg);
 #endif
+#endif
 void flashcache_pid_expiry_all_locked(struct cache_c *dmc);
 int flashcache_uncacheable(struct cache_c *dmc, struct bio *bio);
 void seq_io_remove_from_lru(struct cache_c *dmc, struct sequential_io *seqio);

src/utils/flashcache_setioctl.c

@@ -33,6 +33,7 @@
 #include <sys/types.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <errno.h>
 #include <linux/types.h>
 #include <flashcache_ioctl.h>
 
@@ -42,6 +43,55 @@ void usage(char *pname)
 	exit(1);
 }
 
+void dm_message(char *cachedev, char list, char action, pid_t pid)
+{
+	char pidstr[32];
+
+	char *argv[] = {
+		"/sbin/dmsetup",
+		"message",
+		cachedev,
+		"0",
+		/* command */ NULL,
+		/* sub-command */ NULL,
+		/* pid */ NULL,
+		NULL,
+	};
+
+	switch (list) {
+	case 'w':
+		argv[4] = "whitelist";
+		break;
+	case 'b':
+		argv[4] = "blacklist";
+		break;
+	default:
+		return;
+	}
+
+	switch (action) {
+	case 'a':
+		argv[5] = "add";
+		break;
+	case 'r':
+		argv[5] = "del";
+		break;
+	case 'c':
+		argv[5] = "delall";
+		break;
+	}
+
+	switch (action) {
+	case 'a':
+	case 'r':
+		snprintf(pidstr, sizeof(pidstr), "%lld", (long long)pid);
+		argv[6] = pidstr;
+		break;
+	}
+
+	execv(argv[0], argv);
+}
+
 int
 main(int argc, char **argv)
 {
@@ -50,6 +100,7 @@ main(int argc, char **argv)
 	intmax_t pidmax;
 	char *tmp;
 	pid_t pid;
+	int err;
 
 	while ((c = getopt(argc, argv, "carb:w:")) != -1) {
 		switch (c) {
@@ -125,11 +176,18 @@ main(int argc, char **argv)
 				break;
 		}
 	}
+	err = errno;
 	close(cache_fd);
+	/*
+	 * Failed with an error indicating the ioctl was not appropriate for the device
+	 * switch to using DM messages.
+	 */
+	if (result < 0 && err == ENOTTY) {
+		dm_message(cachedev, list, action, pid);
+	}
 	if (result < 0) {
 		fprintf(stderr, "ioctl failed on %s\n", cachedev);
 		exit(1);
 	}
 	return 0;
 }
-