Use more efficient way of restoring working directory

Rather than using a string-based path, we can restore the working
directory via a file descriptor and use of fchdir().

From the getcwd manpage:
    Opening the current directory (".") and calling fchdir(2) to
    return is usually a faster and more reliable alternative when
    sufficiently many file descriptors are available.

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

3 files changed, 37 insertions, 24 deletions

diff --git a/lib/libalpm/add.c b/lib/libalpm/add.c
index b526145a..eb05f841 100644
--- a/lib/libalpm/add.c
+++ b/lib/libalpm/add.c
@@ -25,6 +25,7 @@
 #include <time.h>
 #include <string.h>
 #include <limits.h>
+#include <fcntl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -528,8 +529,7 @@ static int commit_single_pkg(alpm_handle_t *handle, alpm_pkg_t *newpkg,
 	if(!(trans->flags & ALPM_TRANS_FLAG_DBONLY)) {
 		struct archive *archive;
 		struct archive_entry *entry;
-		char cwd[PATH_MAX] = "";
-		int restore_cwd = 0;
+		int cwdfd;
 
 		_alpm_log(handle, ALPM_LOG_DEBUG, "extracting files\n");
 
@@ -551,10 +551,11 @@ static int commit_single_pkg(alpm_handle_t *handle, alpm_pkg_t *newpkg,
 		}
 
 		/* save the cwd so we can restore it later */
-		if(getcwd(cwd, PATH_MAX) == NULL) {
+		do {
+			cwdfd = open(".", O_RDONLY);
+		} while(cwdfd == -1 && errno == EINTR);
+		if(cwdfd < 0) {
 			_alpm_log(handle, ALPM_LOG_ERROR, _("could not get current working directory\n"));
-		} else {
-			restore_cwd = 1;
 		}
 
 		/* libarchive requires this for extracting hard links */
@@ -607,8 +608,12 @@ static int commit_single_pkg(alpm_handle_t *handle, alpm_pkg_t *newpkg,
 		archive_read_finish(archive);
 
 		/* restore the old cwd if we have it */
-		if(restore_cwd && chdir(cwd) != 0) {
-			_alpm_log(handle, ALPM_LOG_ERROR, _("could not change directory to %s (%s)\n"), cwd, strerror(errno));
+		if(cwdfd >= 0) {
+			if(fchdir(cwdfd) != 0) {
+				_alpm_log(handle, ALPM_LOG_ERROR,
+						_("could not restore working directory (%s)\n"), strerror(errno));
+			}
+			close(cwdfd);
 		}
 
 		if(errors) {
diff --git a/lib/libalpm/handle.c b/lib/libalpm/handle.c
index 5fb4f2bb..dcd81cea 100644
--- a/lib/libalpm/handle.c
+++ b/lib/libalpm/handle.c
@@ -115,7 +115,7 @@ int _alpm_handle_lock(alpm_handle_t *handle)
 	do {
 		fd = open(handle->lockfile, O_WRONLY | O_CREAT | O_EXCL, 0000);
 	} while(fd == -1 && errno == EINTR);
-	if(fd > 0) {
+	if(fd >= 0) {
 		FILE *f = fdopen(fd, "w");
 		fprintf(f, "%ld\n", (long)getpid());
 		fflush(f);
diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
index f4fecabb..e2f2f441 100644
--- a/lib/libalpm/util.c
+++ b/lib/libalpm/util.c
@@ -31,6 +31,7 @@
 #include <unistd.h>
 #include <ctype.h>
 #include <dirent.h>
+#include <fcntl.h>
 #include <time.h>
 #include <syslog.h>
 #include <errno.h>
@@ -277,8 +278,7 @@ int _alpm_unpack(alpm_handle_t *handle, const char *archive, const char *prefix,
 	mode_t oldmask;
 	struct archive *_archive;
 	struct archive_entry *entry;
-	char cwd[PATH_MAX];
-	int restore_cwd = 0;
+	int cwdfd;
 
 	if((_archive = archive_read_new()) == NULL) {
 		RET_ERR(handle, ALPM_ERR_LIBARCHIVE, 1);
@@ -297,10 +297,11 @@ int _alpm_unpack(alpm_handle_t *handle, const char *archive, const char *prefix,
 	oldmask = umask(0022);
 
 	/* save the cwd so we can restore it later */
-	if(getcwd(cwd, PATH_MAX) == NULL) {
+	do {
+		cwdfd = open(".", O_RDONLY);
+	} while(cwdfd == -1 && errno == EINTR);
+	if(cwdfd < 0) {
 		_alpm_log(handle, ALPM_LOG_ERROR, _("could not get current working directory\n"));
-	} else {
-		restore_cwd = 1;
 	}
 
 	/* just in case our cwd was removed in the upgrade operation */
@@ -365,10 +366,14 @@ int _alpm_unpack(alpm_handle_t *handle, const char *archive, const char *prefix,
 cleanup:
 	umask(oldmask);
 	archive_read_finish(_archive);
-	if(restore_cwd && chdir(cwd) != 0) {
-		_alpm_log(handle, ALPM_LOG_ERROR, _("could not change directory to %s (%s)\n"),
-				cwd, strerror(errno));
+	if(cwdfd >= 0) {
+		if(fchdir(cwdfd) != 0) {
+			_alpm_log(handle, ALPM_LOG_ERROR,
+					_("could not restore working directory (%s)\n"), strerror(errno));
+		}
+		close(cwdfd);
 	}
+
 	return ret;
 }
 
@@ -490,17 +495,16 @@ int _alpm_logaction(alpm_handle_t *handle, const char *fmt, va_list args)
 
 int _alpm_run_chroot(alpm_handle_t *handle, const char *path, char *const argv[])
 {
-	char cwd[PATH_MAX];
 	pid_t pid;
-	int pipefd[2];
-	int restore_cwd = 0;
+	int pipefd[2], cwdfd;
 	int retval = 0;
 
 	/* save the cwd so we can restore it later */
-	if(getcwd(cwd, PATH_MAX) == NULL) {
+	do {
+		cwdfd = open(".", O_RDONLY);
+	} while(cwdfd == -1 && errno == EINTR);
+	if(cwdfd < 0) {
 		_alpm_log(handle, ALPM_LOG_ERROR, _("could not get current working directory\n"));
-	} else {
-		restore_cwd = 1;
 	}
 
 	/* just in case our cwd was removed in the upgrade operation */
@@ -598,8 +602,12 @@ int _alpm_run_chroot(alpm_handle_t *handle, const char *path, char *const argv[]
 	}
 
 cleanup:
-	if(restore_cwd && chdir(cwd) != 0) {
-		_alpm_log(handle, ALPM_LOG_ERROR, _("could not change directory to %s (%s)\n"), cwd, strerror(errno));
+	if(cwdfd >= 0) {
+		if(fchdir(cwdfd) != 0) {
+			_alpm_log(handle, ALPM_LOG_ERROR,
+					_("could not restore working directory (%s)\n"), strerror(errno));
+		}
+		close(cwdfd);
 	}
 
 	return retval;