[Quilt-dev] [PATCH 29/39] backup-files: Try mass link/copy first on restore

[Jean Delvare]

When restoring all files from a backup directory, try a mass link (or
copy) first, as it is much faster. It is however not portable and may
thus fail. If it fails, fallback to per-file processing, which always
works.

This change results in a huge performance boost on systems where
the cp command supports all the required options (which includes
all systems using GNU coreutils.)

Signed-off-by: Jean Delvare <address@hidden>
Reviewed-by: Raphael Hertzog <address@hidden>
---
 quilt/scripts/backup-files.in |   26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

--- a/quilt/scripts/backup-files.in
+++ b/quilt/scripts/backup-files.in
@@ -170,12 +170,28 @@ restore_all()
        fi
 
        if [ -s "$NONEMPTY_FILES" ]; then
-               xargs -0 rm -f < "$NONEMPTY_FILES"
+               # Try a mass link (or copy) first, as it is much faster.
+               # It is however not portable and may thus fail. If it fails,
+               # fallback to per-file processing, which always works.
+               local target_dir=$PWD opt_l=-l
+               [ -n "$OPT_NOLINKS" ] && opt_l=-p
 
-               while read -d $'\0' -r
-               do
-                       restore_fast "${REPLY#./}"
-               done < "$NONEMPTY_FILES"
+               if (cd "$OPT_PREFIX" && \
+                   xargs -0 cp $opt_l --parents --remove-destination \
+                               --target-directory="$target_dir" \
+                               < "$NONEMPTY_FILES" 2> /dev/null); then
+                       while read -d $'\0' -r
+                       do
+                               $ECHO "Restoring ${REPLY#./}"
+                       done < "$NONEMPTY_FILES"
+               else
+                       xargs -0 rm -f < "$NONEMPTY_FILES"
+
+                       while read -d $'\0' -r
+                       do
+                               restore_fast "${REPLY#./}"
+                       done < "$NONEMPTY_FILES"
+               fi
 
                if [ -n "$OPT_TOUCH" ]; then
                        xargs -0 touch -c < "$NONEMPTY_FILES"