[dpkg] 114/200: u-a: Use areadlink() instead of lstat() + xreadlink()

[Ximin Luo]

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commit 3d975af556d69a32db7857d5a4141c5f823ca180
Author: Guillem Jover <guillem at debian.org>
Date:   Sun Jan 8 13:33:38 2017 +0100

    u-a: Use areadlink() instead of lstat() + xreadlink()
    
    We avoid an lstat() call as we catch the error from areadlink and can
    react on that instead of an uncontrolled failure from xreadlink().
---
 debian/changelog            |  1 +
 utils/update-alternatives.c | 11 ++---------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/debian/changelog b/debian/changelog
index 4d2d121..91ce6e3 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -10,6 +10,7 @@ dpkg (1.18.19) UNRELEASED; urgency=medium
   * Always set SOURCE_DATE_EPOCH in dpkg-buildpackage and dpkg-source. Use
     the current date if the changelog does not have one. Closes: #849081
   * Refactor update-alternatives pathname existence check into a new function.
+  * Avoid useless repeated lstat()s in update-alternatives.
   * Portability:
     - On GNU/Hurd try to use the new process executable name attribute from
       libps, to properly match on start-stop-daemon --exec.
diff --git a/utils/update-alternatives.c b/utils/update-alternatives.c
index 65b9287..9a9d10c 100644
--- a/utils/update-alternatives.c
+++ b/utils/update-alternatives.c
@@ -1408,7 +1408,6 @@ alternative_set_current(struct alternative *a, char *new_choice)
 static const char *
 alternative_get_current(struct alternative *a)
 {
-	struct stat st;
 	char *curlink;
 	char *file;
 
@@ -1416,15 +1415,9 @@ alternative_get_current(struct alternative *a)
 		return a->current;
 
 	curlink = xasprintf("%s/%s", altdir, a->master_name);
-	if (lstat(curlink, &st)) {
-		if (errno == ENOENT) {
-			free(curlink);
-			return alternative_set_current(a, NULL);
-		}
+	file = areadlink(curlink);
+	if (file == NULL && errno != ENOENT)
 		syserr(_("cannot stat file '%s'"), curlink);
-	}
-
-	file = xreadlink(curlink);
 	free(curlink);
 
 	return alternative_set_current(a, file);

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