[pacman-dev] [PATCH] pacman/query.c : -Qo optimization.

[Chantry Xavier]

I didn't understand why realpath was called on every files of every filelist
in query_fileowner :
ppath = resolve_path(path);

It turns out this is needed for the diverted files. For example, cddb_get
installs /usr/lib/perl5/site_perl/5.8.8/CDDB_get.pm which actually ends in
/usr/lib/perl5/site_perl/current/CDDB_get.pm .

And for making pacman -Qo /usr/lib/perl5/site_perl/current/CDDB_get.pm ,
realpath has to be called on both the target, and the file in the filelist.

However, realpath is costly, and calling it on every single file resulted
in a poor -Qo performance. Worst case :
pacman -Qo /lib/libz.so.1  0.35s user 1.51s system 99% cpu 1.864 total

So I did a little optimization to avoid calling realpath as much as
possible: first compare the basename of each file.

Result:
src/pacman/pacman -Qo /lib/libz.so.1  0.24s user 0.05s system 99% cpu 0.298 total

Obviously, the difference will be even bigger at the first run (no fs
cache), though it's quite scary on my system : 1.7s vs 40s previously.

Signed-off-by: Chantry Xavier <shiningxc at gmail.com>
---
 src/pacman/query.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/src/pacman/query.c b/src/pacman/query.c
index bb69527..7989756 100644
--- a/src/pacman/query.c
+++ b/src/pacman/query.c
@@ -71,6 +71,7 @@ static int query_fileowner(alpm_list_t *targets)
 	for(t = targets; t; t = alpm_list_next(t)) {
 		int found = 0;
 		char *filename = alpm_list_getdata(t);
+		char *bname;
 		char *rpath;
 		struct stat buf;
 		alpm_list_t *i, *j;
@@ -88,6 +89,8 @@ static int query_fileowner(alpm_list_t *targets)
 			continue;
 		}
 
+		bname = basename(filename);
+
 		if(!(rpath = resolve_path(filename))) {
 			fprintf(stderr, _("error: cannot determine real path for '%s': %s\n"),
 					filename, strerror(errno));
@@ -103,6 +106,11 @@ static int query_fileowner(alpm_list_t *targets)
 				snprintf(path, PATH_MAX, "%s%s",
 				         alpm_option_get_root(), (const char *)alpm_list_getdata(j));
 
+				/* avoid the costly resolve_path usage if the basenames don't match */
+				if(strcmp(basename(path), bname) != 0) {
+					continue;
+				}
+
 				ppath = resolve_path(path);
 
 				if(ppath && strcmp(ppath, rpath) == 0) {
-- 
1.5.3.6