io: use sync io if aio fails

io_setup() for aio may fail if a system has reached the
aio request limit.  In this case, fall back to using
sync io.  Also, lvm use of aio can be disabled entirely
with config setting global/use_aio=0.

The system limit for aio requests can be seen from
  /proc/sys/fs/aio-max-nr

The current usage of aio requests can be seen from
  /proc/sys/fs/aio-nr

The system limit for aio requests can be increased by
setting fs.aio-max-nr using sysctl.

Also add last-byte limit to the sync io code.

lib/commands/toolcontext.c

@@ -331,6 +331,8 @@ static void _init_logging(struct cmd_context *cmd)
 	    find_config_tree_bool(cmd, global_test_CFG, NULL);
 	init_test(cmd->default_settings.test);
 
+	init_use_aio(find_config_tree_bool(cmd, global_use_aio_CFG, NULL));
+
 	/* Settings for logging to file */
 	if (find_config_tree_bool(cmd, log_overwrite_CFG, NULL))
 		append = 0;

lib/config/config_settings.h

@@ -1003,6 +1003,9 @@ cfg(global_use_lvmetad_CFG, "use_lvmetad", global_CFG_SECTION, 0, CFG_TYPE_BOOL,
 cfg(global_lvmetad_update_wait_time_CFG, "lvmetad_update_wait_time", global_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_INT, 0, vsn(2, 2, 151), NULL, vsn(3, 0, 0), NULL,
 	"This setting is no longer used.\n")
 
+cfg(global_use_aio_CFG, "use_aio", global_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_BOOL, DEFAULT_USE_AIO, vsn(2, 2, 183), NULL, 0, NULL,
+	"Use async I/O when reading and writing devices.\n")
+
 cfg(global_use_lvmlockd_CFG, "use_lvmlockd", global_CFG_SECTION, 0, CFG_TYPE_BOOL, 0, vsn(2, 2, 124), NULL, 0, NULL,
 	"Use lvmlockd for locking among hosts using LVM on shared storage.\n"
 	"Applicable only if LVM is compiled with lockd support in which\n"

lib/config/defaults.h

@@ -60,6 +60,7 @@
 #define DEFAULT_METADATA_READ_ONLY 0
 #define DEFAULT_LVDISPLAY_SHOWS_FULL_DEVICE_PATH 0
 #define DEFAULT_UNKNOWN_DEVICE_NAME "[unknown]"
+#define DEFAULT_USE_AIO 1
 
 #define DEFAULT_SANLOCK_LV_EXTEND_MB 256
 

lib/device/bcache.c

@@ -389,6 +389,48 @@ static bool _sync_issue(struct io_engine *ioe, enum dir d, int fd,
         	return false;
 	}
 
+	/*
+	 * If bcache block goes past where lvm wants to write, then clamp it.
+	 */
+	if ((d == DIR_WRITE) && _last_byte_offset && (fd == _last_byte_fd)) {
+		uint64_t offset = where;
+		uint64_t nbytes = len;
+		sector_t limit_nbytes = 0;
+		sector_t extra_nbytes = 0;
+
+		if (offset > _last_byte_offset) {
+			log_error("Limit write at %llu len %llu beyond last byte %llu",
+				  (unsigned long long)offset,
+				  (unsigned long long)nbytes,
+				  (unsigned long long)_last_byte_offset);
+			return false;
+		}
+
+		if (offset + nbytes > _last_byte_offset) {
+			limit_nbytes = _last_byte_offset - offset;
+			if (limit_nbytes % _last_byte_sector_size)
+				extra_nbytes = _last_byte_sector_size - (limit_nbytes % _last_byte_sector_size);
+
+			if (extra_nbytes) {
+				log_debug("Limit write at %llu len %llu to len %llu rounded to %llu",
+					  (unsigned long long)offset,
+					  (unsigned long long)nbytes,
+					  (unsigned long long)limit_nbytes,
+					  (unsigned long long)(limit_nbytes + extra_nbytes));
+				nbytes = limit_nbytes + extra_nbytes;
+			} else {
+				log_debug("Limit write at %llu len %llu to len %llu",
+					  (unsigned long long)offset,
+					  (unsigned long long)nbytes,
+					  (unsigned long long)limit_nbytes);
+				nbytes = limit_nbytes;
+			}
+		}
+
+		where = offset;
+		len = nbytes;
+	}
+
 	while (len) {
         	do {
                 	if (d == DIR_READ)

lib/label/label.c

@@ -799,7 +799,7 @@ out:
 
 static int _setup_bcache(int cache_blocks)
 {
-	struct io_engine *ioe;
+	struct io_engine *ioe = NULL;
 
 	if (cache_blocks < MIN_BCACHE_BLOCKS)
 		cache_blocks = MIN_BCACHE_BLOCKS;
@@ -807,9 +807,18 @@ static int _setup_bcache(int cache_blocks)
 	if (cache_blocks > MAX_BCACHE_BLOCKS)
 		cache_blocks = MAX_BCACHE_BLOCKS;
 
-	if (!(ioe = create_async_io_engine())) {
+	if (use_aio()) {
-		log_error("Failed to create bcache io engine.");
+		if (!(ioe = create_async_io_engine())) {
-		return 0;
+			log_warn("Failed to set up async io, using sync io.");
+			init_use_aio(0);
+		}
+	}
+
+	if (!ioe) {
+		if (!(ioe = create_sync_io_engine())) {
+			log_error("Failed to set up sync io.");
+			return 0;
+		}
 	}
 
 	if (!(scan_bcache = bcache_create(BCACHE_BLOCK_SIZE_IN_SECTORS, cache_blocks, ioe))) {

lib/misc/lvm-globals.c

@@ -24,6 +24,7 @@
 static int _verbose_level = VERBOSE_BASE_LEVEL;
 static int _silent = 0;
 static int _test = 0;
+static int _use_aio = 0;
 static int _md_filtering = 0;
 static int _internal_filtering = 0;
 static int _fwraid_filtering = 0;
@@ -69,6 +70,11 @@ void init_test(int level)
 	_test = level;
 }
 
+void init_use_aio(int use_aio)
+{
+	_use_aio = use_aio;
+}
+
 void init_md_filtering(int level)
 {
 	_md_filtering = level;
@@ -215,6 +221,11 @@ int test_mode(void)
 	return _test;
 }
 
+int use_aio(void)
+{
+	return _use_aio;
+}
+
 int md_filtering(void)
 {
 	return _md_filtering;

lib/misc/lvm-globals.h

@@ -25,6 +25,7 @@ enum dev_ext_e;
 void init_verbose(int level);
 void init_silent(int silent);
 void init_test(int level);
+void init_use_aio(int use_aio);
 void init_md_filtering(int level);
 void init_internal_filtering(int level);
 void init_fwraid_filtering(int level);
@@ -55,6 +56,7 @@ const char *get_cmd_name(void);
 void set_sysfs_dir_path(const char *path);
 
 int test_mode(void);
+int use_aio(void);
 int md_filtering(void);
 int internal_filtering(void);
 int fwraid_filtering(void);