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.

2 files changed, 13 insertions, 0 deletions

diff --git a/lib/misc/lvm-globals.c b/lib/misc/lvm-globals.c
index 86e6cf49f..0ad60fd93 100644
--- a/lib/misc/lvm-globals.c
+++ b/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;
diff --git a/lib/misc/lvm-globals.h b/lib/misc/lvm-globals.h
index 6fc26ccc4..42dcc341e 100644
--- a/lib/misc/lvm-globals.h
+++ b/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);