Add optional locking to swift-ring-builder

If invoked as 'swift-ring-builder-safe' the directory containing the builder
file provided will be locked (via lock_parent_directory()). This provides a
small safe guard against multiple instances of the swift-ring-builder (or
other utilities that observe this lock) from attempting to write to or read
the builder/ring files while operations are in progress.

This is particularly useful in environments where ring management has been
automated (via Chef or custom solutions) but the operator still occasionally
needs to manually interact with the ring.

DocImpact

Change-Id: Ia362744a8151a91bfb586d01da582906726852e6

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/manpages/swift-ring-builder.1 b/doc/manpages/swift-ring-builder.1
index c8433e8dd..59f7736e7 100644
--- a/doc/manpages/swift-ring-builder.1
+++ b/doc/manpages/swift-ring-builder.1
@@ -48,6 +48,14 @@ partitions will end up assigned to different devices, and therefore nearly all
 data stored will have to be replicated to new locations. So, recovery from a
 builder file loss is possible, but data will definitely be unreachable for an
 extended time.
+.PP
+If invoked as 'swift-ring-builder-safe' the directory containing the builder
+file provided will be locked (via a .lock file in the files parent directory).
+This provides a basic safe guard against multiple instances of the swift-ring-builder
+(or other utilities that observe this lock) from attempting to write to or read
+the builder/ring files while operations are in progress. This can be useful in
+environments where ring management has been automated but the operator still
+needs to interact with the rings manually.
 
 
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