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Commits › b64f9dd
backup libraries: atomic replacement of the library
Baptiste Daroussin committed 22 days ago
commit b64f9dd2156664c6205b318ce0815c53b2e119aa
parent c79dfc9
1 file changed +40 -16
modified libpkg/backup_lib.c
@@ -133,6 +133,7 @@ backup_library(struct pkgdb *db, struct pkg *p, const char *path)
{

	const char *libname;

	const char *bkpath;
+ 
	const char *rootdir;

	int from, to, backupdir;



	if ((libname = strrchr(path, '/')) == NULL)
@@ -167,27 +168,48 @@ backup_library(struct pkgdb *db, struct pkg *p, const char *path)
	}



	/*
- 
	 * always overwrite the existing backup library, it might be older than
- 
	 * this one
+ 
	 * Write to a temporary file and atomically rename into place.
+ 
	 * This avoids corrupting or removing a backup library that may
+ 
	 * still be in use if the process is interrupted.

	 */
- 
	/* first always unlink to ensure we are not truncating a used library */
- 
	unlinkat(backupdir, libname, 0);
- 
	to = openat(backupdir, libname, O_EXCL|O_CREAT|O_WRONLY, 0644);
+ 
	char tmpname[MAXPATHLEN];
+ 
	char tmppath[MAXPATHLEN];
+ 
	rootdir = ctx.pkg_rootdir != NULL ? ctx.pkg_rootdir : "";
+ 
	snprintf(tmpname, sizeof(tmpname), ".%s.XXXXXX", libname);
+ 
	snprintf(tmppath, sizeof(tmppath), "%s%s/%s", rootdir, bkpath, tmpname);
+ 
	to = mkstemp(tmppath);
+ 
	/* Update tmpname with the resolved XXXXXX suffix */
+ 
	strlcpy(tmpname, strrchr(tmppath, '/') + 1, sizeof(tmpname));

	if (to == -1) {
- 
		pkg_emit_errno("Unable to create the backup library", libname);
+ 
		pkg_emit_errno("Unable to create temporary backup library",
+ 
		    libname);
+ 
		goto out;
+ 
	}
+ 
	if (fchmod(to, 0644) == -1) {
+ 
		pkg_emit_errno("Unable to set permissions on backup library",
+ 
		    libname);

		goto out;

	}
- 
	if (pkg_copy_file(from, to)) {
- 
		if (close(to) < 0) {
- 
			to = -1;
- 
			goto out;
- 
		}
- 
		close(from);
- 
		register_backup(db, p, backupdir, libname);
- 
		close(backupdir);
- 
		return;
+ 
	if (!pkg_copy_file(from, to))
+ 
		goto out;
+ 
	if (close(to) < 0) {
+ 
		to = -1;
+ 
		goto out;

	}
+ 
	to = -1;
+ 
	close(from);
+ 
	from = -1;
+
+ 
	if (renameat(backupdir, tmpname, backupdir, libname) == -1) {
+ 
		pkg_emit_errno("Unable to rename backup library", libname);
+ 
		unlinkat(backupdir, tmpname, 0);
+ 
		goto out;
+ 
	}
+
+ 
	register_backup(db, p, backupdir, libname);
+ 
	close(backupdir);
+ 
	return;



out:

	pkg_emit_errno("Failed to backup the library", libname);
@@ -195,8 +217,10 @@ out:
		close(backupdir);

	if (from >= 0)

		close(from);
- 
	if (to >= 0)
+ 
	if (to >= 0) {
+ 
		unlinkat(backupdir, tmpname, 0);

		close(to);
+ 
	}

}



/*