Introduce xbps_repo_{un,}lock() to serialize write access to repodata.

We use a simple file lock that is created with O_CREAT|O_EXCL.
This should fix the concurrency issues with multiple processes
running xbps-rindex -a/-c on the same repository/arch combo.

bin/xbps-rindex/index-add.c

@@ -43,8 +43,8 @@ index_add(struct xbps_handle *xhp, int args, int argmax, char **argv, bool force
 	xbps_dictionary_t idx, idxmeta, binpkgd, curpkgd;
 	struct xbps_repo *repo = NULL;
 	struct stat st;
-	char *tmprepodir = NULL, *repodir = NULL;
-	int rv = 0, ret = 0;
+	char *tmprepodir = NULL, *repodir = NULL, *rlockfname = NULL;
+	int rv = 0, ret = 0, rlockfd = -1;
 	bool flush = false;
 
 	assert(argv);
@@ -55,7 +55,13 @@ index_add(struct xbps_handle *xhp, int args, int argmax, char **argv, bool force
 		return ENOMEM;
 
 	repodir = dirname(tmprepodir);
-	repo = xbps_repo_open(xhp, repodir, true);
+	if (!xbps_repo_lock(xhp, repodir, &rlockfd, &rlockfname)) {
+		fprintf(stderr, "xbps-rindex: cannot lock repository "
+		    "%s: %s\n", repodir, strerror(errno));
+		rv = -1;
+		goto out;
+	}
+	repo = xbps_repo_open(xhp, repodir);
 	if (repo == NULL && errno != ENOENT) {
 		fprintf(stderr, "xbps-rindex: cannot open/lock repository "
 		    "%s: %s\n", repodir, strerror(errno));
@@ -217,6 +223,9 @@ index_add(struct xbps_handle *xhp, int args, int argmax, char **argv, bool force
 out:
 	if (repo)
 		xbps_repo_close(repo);
+
+	xbps_repo_unlock(rlockfd, rlockfname);
+
 	if (tmprepodir)
 		free(tmprepodir);
 

bin/xbps-rindex/index-clean.c

@@ -96,10 +96,17 @@ index_clean(struct xbps_handle *xhp, const char *repodir)
 	xbps_dictionary_t idx = NULL, idxmeta = NULL;
 	struct xbps_repo *repo;
 	struct cbdata cbd;
-	int rv = 0;
+	char *rlockfname = NULL;
+	int rv = 0, rlockfd = -1;
 	bool flush = false;
 
-	repo = xbps_repo_open(xhp, repodir, true);
+	if (!xbps_repo_lock(xhp, repodir, &rlockfd, &rlockfname)) {
+		rv = errno;
+		fprintf(stderr, "%s: cannot lock repository: %s\n",
+		    _XBPS_RINDEX, strerror(rv));
+		return rv;
+	}
+	repo = xbps_repo_open(xhp, repodir);
 	if (repo == NULL) {
 		rv = errno;
 		if (rv == ENOENT)
@@ -156,6 +163,8 @@ index_clean(struct xbps_handle *xhp, const char *repodir)
 
 out:
 	xbps_repo_close(repo);
+	xbps_repo_unlock(rlockfd, rlockfname);
+
 	if (idx)
 		xbps_object_release(idx);
 	if (idxmeta)

bin/xbps-rindex/remove-obsoletes.c

@@ -118,7 +118,7 @@ remove_obsoletes(struct xbps_handle *xhp, const char *repodir)
 	char *ext;
 	int rv = 0;
 
-	repo = xbps_repo_open(xhp, repodir, false);
+	repo = xbps_repo_open(xhp, repodir);
 	if (repo == NULL) {
 		if (errno != ENOENT) {
 			fprintf(stderr, "xbps-rindex: cannot read repository data: %s\n",

bin/xbps-rindex/sign.c

@@ -119,7 +119,7 @@ sign_repo(struct xbps_handle *xhp, const char *repodir,
 	const char *privkey, const char *signedby)
 {
 	struct stat st;
-	struct xbps_repo *repo;
+	struct xbps_repo *repo = NULL;
 	xbps_dictionary_t pkgd, meta = NULL;
 	xbps_data_t data = NULL, rpubkey = NULL;
 	xbps_object_iterator_t iter = NULL;
@@ -129,8 +129,9 @@ sign_repo(struct xbps_handle *xhp, const char *repodir,
 	unsigned int siglen;
 	uint16_t rpubkeysize, pubkeysize;
 	const char *arch, *pkgver, *rsignedby = NULL;
-	char *binpkg = NULL, *binpkg_sig = NULL, *buf = NULL, *defprivkey = NULL;
-	int binpkg_fd, binpkg_sig_fd, rv = 0;
+	char *binpkg = NULL, *binpkg_sig = NULL, *buf = NULL;
+	char *rlockfname = NULL, *defprivkey = NULL;
+	int binpkg_fd, binpkg_sig_fd, rlockfd = -1, rv = 0;
 	bool flush = false;
 
 	if (signedby == NULL) {
@@ -141,7 +142,13 @@ sign_repo(struct xbps_handle *xhp, const char *repodir,
 	/*
 	 * Check that repository index exists and not empty, otherwise bail out.
 	 */
-	repo = xbps_repo_open(xhp, repodir, true);
+	if (!xbps_repo_lock(xhp, repodir, &rlockfd, &rlockfname)) {
+		rv = errno;
+		fprintf(stderr, "%s: cannot lock repository: %s\n",
+		    _XBPS_RINDEX, strerror(errno));
+		goto out;
+	}
+	repo = xbps_repo_open(xhp, repodir);
 	if (repo == NULL) {
 		rv = errno;
 		fprintf(stderr, "%s: cannot read repository data: %s\n",
@@ -304,5 +311,7 @@ out:
 	if (repo) {
 		xbps_repo_close(repo);
 	}
+	xbps_repo_unlock(rlockfd, rlockfname);
+
 	return rv ? -1 : 0;
 }

include/xbps.h.in

@@ -48,7 +48,7 @@
  *
  * This header documents the full API for the XBPS Library.
  */
-#define XBPS_API_VERSION	"20150219-1"
+#define XBPS_API_VERSION	"20150323"
 
 #ifndef XBPS_VERSION
  #define XBPS_VERSION		"UNSET"
@@ -1265,7 +1265,6 @@ struct xbps_repo {
 	 * @private
 	 */
 	int fd;
-	bool is_locked;
 	/**
 	 * var is_remote
 	 *
@@ -1412,16 +1411,36 @@ xbps_dictionary_t xbps_rpool_get_pkg_plist(struct xbps_handle *xhp,
  */
 bool xbps_repo_store(struct xbps_handle *xhp, const char *url);
 
+/**
+ * Creates a lock for a local repository to obtain exclusive access (write).
+ *
+ * @param[in] xhp Pointer to the xbps_handle struct.
+ * @param[in] uri Repository URI to match.
+ * @param[out] lockfd Lock file descriptor assigned.
+ * @param[out] lockfname Lock filename assigned.
+ *
+ * @return True on success and lockfd/lockfname are assigned appropiately.
+ * otherwise false and lockfd/lockfname aren't set.
+ */
+bool xbps_repo_lock(struct xbps_handle *xhp, const char *uri, int *lockfd, char **lockfname);
+
+/**
+ * Unlocks a local repository and removes its lock file.
+ *
+ * @param[in] lockfd Lock file descriptor.
+ * @param[in] lockfname Lock filename.
+ */
+void xbps_repo_unlock(int lockfd, char *lockfname);
+
 /**
  * Opens a repository and returns a xbps_repo object.
  *
  * @param[in] xhp Pointer to the xbps_handle struct.
  * @param[in] uri Repository URI to match.
- * @param[in] lock Set it to true to acquire a POSIX file lock.
  *
  * @return The matching repository object, NULL otherwise.
  */
-struct xbps_repo *xbps_repo_open(struct xbps_handle *xhp, const char *url, bool lock);
+struct xbps_repo *xbps_repo_open(struct xbps_handle *xhp, const char *url);
 
 /**
  * Closes a repository object and releases resources.

lib/repo.c

@@ -73,22 +73,61 @@ repo_get_dict(struct xbps_repo *repo)
 	return xbps_archive_get_dictionary(repo->ar, entry);
 }
 
+bool
+xbps_repo_lock(struct xbps_handle *xhp, const char *repodir,
+		int *lockfd, char **lockfname)
+{
+	char *repofile, *lockfile;
+	int fd, rv;
+
+	assert(repodir);
+	assert(lockfd);
+	assert(lockfname);
+
+	repofile = xbps_repo_path(xhp, repodir);
+	assert(repofile);
+
+	lockfile = xbps_xasprintf("%s.lock", repofile);
+	free(repofile);
+
+	for (;;) {
+		fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, 0660);
+		rv = errno;
+		if (fd != -1)
+			break;
+		if (rv != EEXIST) {
+			xbps_dbg_printf(xhp, "[repo] `%s' failed to "
+			    "create lock file %s\n", lockfile, strerror(rv));
+			free(lockfile);
+			return false;
+		} else {
+			xbps_dbg_printf(xhp, "[repo] `%s' lock file exists,"
+			    "waiting...\n", lockfile);
+		}
+	}
+	*lockfname = lockfile;
+	*lockfd = fd;
+	return true;
+}
+
+void
+xbps_repo_unlock(int lockfd, char *lockfname)
+{
+        if (lockfd != -1) {
+		close(lockfd);
+	}
+	if (lockfname) {
+		unlink(lockfname);
+		free(lockfname);
+	}
+}
+
 static bool
-repo_open_local(struct xbps_repo *repo, const char *repofile, bool lock)
+repo_open_local(struct xbps_repo *repo, const char *repofile)
 {
 	struct stat st;
 	int rv = 0;
 
-	/*
-	 * Acquire a POSIX file lock on the archive; wait if the lock is
-	 * already taken.
-	 */
-        if (lock && lockf(repo->fd, F_LOCK, 0) == -1) {
-		rv = errno;
-		xbps_dbg_printf(repo->xhp, "[repo] failed to lock %s: %s\n",
-		    repofile, strerror(rv));
-		return false;
-	}
 	if (fstat(repo->fd, &st) == -1) {
 		rv = errno;
 		xbps_dbg_printf(repo->xhp, "[repo] `%s' fstat repodata %s\n",
@@ -179,7 +218,7 @@ xbps_repo_store(struct xbps_handle *xhp, const char *repo)
 }
 
 struct xbps_repo *
-xbps_repo_open(struct xbps_handle *xhp, const char *url, bool lock)
+xbps_repo_open(struct xbps_handle *xhp, const char *url)
 {
 	struct xbps_repo *repo;
 	const char *arch;
@@ -195,6 +234,7 @@ xbps_repo_open(struct xbps_handle *xhp, const char *url, bool lock)
 
 	repo = calloc(1, sizeof(struct xbps_repo));
 	assert(repo);
+	repo->fd = -1;
 	repo->xhp = xhp;
 	repo->uri = url;
 
@@ -225,31 +265,21 @@ xbps_repo_open(struct xbps_handle *xhp, const char *url, bool lock)
 	/*
 	 * Open the repository archive.
 	 */
-	if (lock) {
-		repo->fd = open(repofile, O_RDWR);
-		repo->is_locked = true;
-	} else {
-		repo->fd = open(repofile, O_RDONLY);
-	}
-
+	repo->fd = open(repofile, O_RDONLY);
 	if (repo->fd == -1) {
 		int rv = errno;
 		xbps_dbg_printf(xhp, "[repo] `%s' open repodata %s\n",
 		    repofile, strerror(rv));
 		goto out;
 	}
-	if (repo_open_local(repo, repofile, lock)) {
+	if (repo_open_local(repo, repofile)) {
 		free(repofile);
 		return repo;
 	}
 
 out:
-	if (repo->ar)
-		archive_read_free(repo->ar);
-	if (repo->fd != -1)
-		close(repo->fd);
 	free(repofile);
-	free(repo);
+	xbps_repo_close(repo);
 	return NULL;
 }
 
@@ -269,10 +299,10 @@ xbps_repo_close(struct xbps_repo *repo)
 		xbps_object_release(repo->idxmeta);
 		repo->idxmeta = NULL;
 	}
-        if (repo->is_locked && lockf(repo->fd, F_ULOCK, 0) == -1)
-		xbps_dbg_printf(repo->xhp, "[repo] failed to unlock %s: %s\n", repo->uri, strerror(errno));
+	if (repo->fd != -1)
+		close(repo->fd);
 
-	close(repo->fd);
+	free(repo);
 }
 
 xbps_dictionary_t

lib/rpool.c

@@ -92,7 +92,7 @@ xbps_regget_repo(struct xbps_handle *xhp, const char *url)
 			if (strcmp(repouri, url))
 				continue;
 
-			repo = xbps_repo_open(xhp, repouri, false);
+			repo = xbps_repo_open(xhp, repouri);
 			if (!repo)
 				return NULL;
 
@@ -148,7 +148,7 @@ xbps_rpool_foreach(struct xbps_handle *xhp,
 	for (unsigned int i = 0; i < xbps_array_count(xhp->repositories); i++) {
 		xbps_array_get_cstring_nocopy(xhp->repositories, i, &repouri);
 		if ((repo = xbps_rpool_get_repo(repouri)) == NULL) {
-			repo = xbps_repo_open(xhp, repouri, false);
+			repo = xbps_repo_open(xhp, repouri);
 			if (!repo)
 				continue;
 			SIMPLEQ_INSERT_TAIL(&rpool_queue, repo, entries);