Fix concurrency issues in pkgdb: only allow 1 write transaction at the same time.

This implementation relies on a POSIX named semaphore, which is also
required by xbps-rindex(8).

NEWS

@@ -1,5 +1,9 @@
 xbps-0.33 (???):
 
+ * Only allow a single writer to the pkgdb to avoid concurrency issues
+   when performing multiple write transactions (install, update or remove).
+   The implementation relies on a POSIX named semaphore.
+
  * Do not continue the transaction if downloading a binpkg/signature file
    has failed for some reason, stop and return error immediately.
 

README.md

@@ -35,6 +35,7 @@ See `git tag -l` to list all available stable releases.
 To build this you'll need:
 
   - A C99 compiler (clang and gcc tested)
+  - A system that supports POSIX named semaphores
   - [GNU make](http://www.gnu.org/software/make/)
   - [pkg-config](http://www.freedesktop.org/wiki/Software/pkg-config/)
   - [zlib](http://www.zlib.net)

TODO

@@ -2,7 +2,6 @@ libxbps:
  - transaction: avoid fetching the whole pkg when updating and only fetch
    modified files from target pkg.
  - Add support to handle 'shlib-requires' and 'shlib-provides'.
- - Concurrency issues with pkgdb.
 
 xbps-create:
  - Move all configuration files to <prefix>/share/<pkgname>/conf/<cffile>.

bin/xbps-install/main.c

@@ -1,5 +1,5 @@
 /*-
- * Copyright (c) 2008-2013 Juan Romero Pardines.
+ * Copyright (c) 2008-2014 Juan Romero Pardines.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -216,6 +216,11 @@ main(int argc, char **argv)
 	if (sync && !update && (argc == optind))
 		exit(EXIT_SUCCESS);
 
+	if ((rv = xbps_pkgdb_lock(&xh)) != 0) {
+		fprintf(stderr, "Failed to lock the pkgdb: %s\n", strerror(rv));
+		exit(rv);
+	}
+
 	if (update && (argc == optind)) {
 		/* Update all installed packages */
 		rv = dist_upgrade(&xh, maxcols, yes, drun);
@@ -223,19 +228,24 @@ main(int argc, char **argv)
 		/* Update target packages */
 		for (i = optind; i < argc; i++) {
 			rv = update_pkg(&xh, argv[i]);
-			if (rv != 0)
+			if (rv != 0) {
+				xbps_pkgdb_unlock(&xh);
 				exit(rv);
+			}
 		}
 		rv = exec_transaction(&xh, maxcols, yes, drun);
 	} else if (!update) {
 		/* Install target packages */
 		for (i = optind; i < argc; i++) {
 			rv = install_new_pkg(&xh, argv[i], reinstall);
-			if (rv != 0)
+			if (rv != 0) {
+				xbps_pkgdb_unlock(&xh);
 				exit(rv);
+			}
 		}
 		rv = exec_transaction(&xh, maxcols, yes, drun);
 	}
 
+	xbps_pkgdb_unlock(&xh);
 	exit(rv);
 }

bin/xbps-pkgdb/main.c

@@ -1,5 +1,5 @@
 /*-
- * Copyright (c) 2013 Juan Romero Pardines.
+ * Copyright (c) 2013-2014 Juan Romero Pardines.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -146,12 +146,17 @@ main(int argc, char **argv)
 		exit(EXIT_FAILURE);
 	}
 
+	if ((rv = xbps_pkgdb_lock(&xh)) != 0) {
+		fprintf(stderr, "failed to lock pkgdb: %s\n", strerror(rv));
+		exit(EXIT_FAILURE);
+	}
 	if (update_format)
 		convert_pkgdb_format(&xh);
 	else if (instmode) {
 		if (argc == optind) {
 			fprintf(stderr,
 			    "xbps-pkgdb: missing PKGNAME argument\n");
+			xbps_pkgdb_unlock(&xh);
 			exit(EXIT_FAILURE);
 		}
 		for (i = optind; i < argc; i++) {
@@ -160,6 +165,7 @@ main(int argc, char **argv)
 				fprintf(stderr, "xbps-pkgdb: failed to "
 				    "change to %s mode to %s: %s\n",
 				    instmode, argv[i], strerror(rv));
+				xbps_pkgdb_unlock(&xh);
 				exit(EXIT_FAILURE);
 			}
 		}
@@ -174,5 +180,6 @@ main(int argc, char **argv)
 		}
 	}
 
+	xbps_pkgdb_unlock(&xh);
 	exit(rv ? EXIT_FAILURE : EXIT_SUCCESS);
 }

bin/xbps-remove/main.c

@@ -350,8 +350,14 @@ main(int argc, char **argv)
 			exit(rv);;
 	}
 
+	if ((rv = xbps_pkgdb_lock(&xh)) != 0) {
+		fprintf(stderr, "failed to lock pkgdb: %s\n", strerror(rv));
+		exit(rv);
+	}
+
 	if (orphans) {
 		if ((rv = xbps_transaction_autoremove_pkgs(&xh)) != 0) {
+			xbps_pkgdb_unlock(&xh);
 			if (rv != ENOENT) {
 				fprintf(stderr, "Failed to queue package "
 				    "orphans: %s\n", strerror(rv));
@@ -370,11 +376,13 @@ main(int argc, char **argv)
 		else
 			reqby_force = true;
 	}
-	if (reqby_force && !ignore_revdeps)
+	if (reqby_force && !ignore_revdeps) {
+		xbps_pkgdb_unlock(&xh);
 		exit(EXIT_FAILURE);
-
-	if (orphans || (argc > optind))
+	}
+	if (orphans || (argc > optind)) {
 		rv = exec_transaction(&xh, maxcols, yes, drun);
-
+	}
+	xbps_pkgdb_unlock(&xh);
 	exit(rv);
 }

include/xbps.h.in

@@ -24,13 +24,13 @@
  *-
  */
 
-#ifndef _XBPS_API_H_
-#define _XBPS_API_H_
-
+#ifndef _XBPS_H_
+#define _XBPS_H_
 
 #include <stdio.h>
 #include <inttypes.h>
 #include <limits.h>
+#include <semaphore.h>
 
 #include <xbps/xbps_array.h>
 #include <xbps/xbps_bool.h>
@@ -50,7 +50,7 @@
  *
  * This header documents the full API for the XBPS Library.
  */
-#define XBPS_API_VERSION	"20140130"
+#define XBPS_API_VERSION	"20140223"
 
 #ifndef XBPS_VERSION
  #define XBPS_VERSION		"UNSET"
@@ -475,6 +475,12 @@ struct xbps_handle {
 	 * stored in XBPS_META_PATH/XBPS_PKGDB.
 	 */
 	xbps_dictionary_t pkgdb;
+	/**
+	 * @private
+	 *
+	 * POSIX named semaphore associated with the pkgdb for writers.
+	 */
+	sem_t *pkgdb_sem;
 	/**
 	 * @var transd
 	 *
@@ -706,6 +712,25 @@ xbps_array_t xbps_find_pkg_obsoletes(struct xbps_handle *xhp,
 /** @addtogroup pkgdb */
 /*@{*/
 
+/**
+ * Locks the pkgdb to allow a write transaction.
+ *
+ * This routine should be called before a write transaction is the target:
+ * install, remove or update.
+ *
+ * @param[in] xhp The pointer to the xbps_handle struct.
+ * @return 0 on success, otherwise an errno value.
+ */
+int xbps_pkgdb_lock(struct xbps_handle *);
+
+/**
+ * Unlocks the pkgdb after a write transaction: the POSIX named semaphore
+ * is unlocked and unlinked.
+ *
+ * @param[in] xhp The pointer to the xbps_handle struct.
+ */
+void xbps_pkgdb_unlock(struct xbps_handle *);
+
 /**
  * Executes a function callback per a package dictionary registered
  * in master package database (pkgdb) plist.
@@ -1693,4 +1718,4 @@ char *xbps_pubkey2fp(struct xbps_handle *xhp, xbps_data_t pubkey);
 }
 #endif
 
-#endif /* !_XBPS_API_H_ */
+#endif /* !_XBPS_H_ */

include/xbps_api_impl.h

@@ -1,5 +1,5 @@
 /*-
- * Copyright (c) 2010-2013 Juan Romero Pardines.
+ * Copyright (c) 2010-2014 Juan Romero Pardines.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without

lib/pkgdb.c

@@ -1,5 +1,5 @@
 /*-
- * Copyright (c) 2012-2013 Juan Romero Pardines.
+ * Copyright (c) 2012-2014 Juan Romero Pardines.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -28,6 +28,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <semaphore.h>
 
 #include "xbps_api_impl.h"
 
@@ -54,6 +57,48 @@
  * data type is specified on its edge, i.e array, bool, integer, string,
  * dictionary.
  */
+#define _PKGDB_SEMNAME	"/libxbps-pkgdb"
+int
+xbps_pkgdb_lock(struct xbps_handle *xhp)
+{
+	int rv = 0;
+	mode_t myumask;
+	/*
+	 * Create/open the POSIX named semaphore.
+	 */
+	myumask = umask(0);
+	xhp->pkgdb_sem = sem_open(_PKGDB_SEMNAME, O_CREAT, 0660, 1);
+	umask(myumask);
+
+	if (xhp->pkgdb_sem == SEM_FAILED) {
+		rv = errno;
+		xbps_dbg_printf(xhp, "pkgdb: failed to create/open named "
+		    "semaphore: %s\n", strerror(errno));
+		return rv;
+	}
+	if (sem_wait(xhp->pkgdb_sem) == -1) {
+		rv = errno;
+		xbps_dbg_printf(xhp, "pkgdb: failed to lock named semaphore: %s\n",
+		    strerror(errno));
+		return rv;
+	}
+	return 0;
+}
+
+void
+xbps_pkgdb_unlock(struct xbps_handle *xhp)
+{
+	/* Unlock semaphore, close and destroy it (if possible) */
+	if (xhp->pkgdb_sem == NULL)
+		return;
+
+	sem_post(xhp->pkgdb_sem);
+	sem_close(xhp->pkgdb_sem);
+	sem_unlink(_PKGDB_SEMNAME);
+	xhp->pkgdb_sem = NULL;
+}
+#undef _PKGDB_SEMNAME
+
 int HIDDEN
 xbps_pkgdb_init(struct xbps_handle *xhp)
 {