Allow UseDelta option to specify a delta ratio

Rework the frontend and backend to allow passing a ratio value in for
UseDelta rather than having a hardcoded #define-d 0.7 value always used.
This is useful for those with fast connections, who would likely benefit
from tuning this ratio to lower values; it is also useful for general
testing purposes.

The libalpm API changes for this, but we do support the old config file
format with a no-value 'UseDelta' option; in this case we simply use the
old default of 0.7.

We clamp the ratio values to a sane range between 0.0 and 2.0, allowing
ratios above 1.0 for testing purposes.

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/doc/pacman.conf.5.txt b/doc/pacman.conf.5.txt
index 2c1a24b2..39132925 100644
--- a/doc/pacman.conf.5.txt
+++ b/doc/pacman.conf.5.txt
@@ -168,9 +168,13 @@ Options
 	Log action messages through syslog(). This will insert log entries into
 	+{localstatedir}/log/messages+ or equivalent.
 
-*UseDelta*::
-	Download delta files instead of complete packages if possible.  Requires
-	the xdelta3 program to be installed.
+*UseDelta* [= ratio]::
+	Download delta files instead of complete packages if possible. Requires
+	the `xdelta3` program to be installed. If a ratio is specified (e.g.,
+	`0.5`), then it is used as a cutoff for determining whether to use deltas.
+	Allowed values are between `0.0` and `2.0`; sensible values are between
+	`0.2` and `0.9`.  Using a value above `1.0` is not recommended.  The
+	default is `0.7` if left unspecified.
 
 *TotalDownload*::
 	When downloading, display the amount downloaded, download rate, ETA,