Add a test program to exercise a specific bug - racing unlink/write on a full filesystem

src/Makefile

@@ -37,7 +37,7 @@ TARGETS = alloc acl_get bstat devzero dirstress fault feature \
 	  fill fill2 getpagesize holes xfsctl loggen lstat64 \
 	  nametest permname randholes runas truncfile usemem \
 	  fstest mmapcat append_reader append_writer \
-	  dirperf metaperf
+	  dirperf metaperf enospc_unlink
 ifeq ($(ENABLE_DBM), yes)
 TARGETS += dbtest
 endif

src/enospc_unlink.c

@@ -0,0 +1,78 @@
+/* 
+ * Write a file until filesystem full is reached and then unlink it.
+ * Demonstrates a particular deadlock that Kaz hit in testing.  Run
+ * several iterations of this in parallel on a near-full filesystem.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <malloc.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+int main(int argc, char **argv)
+{
+	int			fd, sz, done;
+	void			*ptr;
+	size_t			written;
+	unsigned int		i, count = 0;
+	unsigned long long	bytes = 0;
+
+	if (argc < 2) {
+		fprintf(stderr, "Insufficient arguments\n");
+		exit(1);
+	}
+	if (argc < 3) {
+		count = (unsigned int)atoi(argv[2]);
+	}
+
+	sz = 1024 * 1024;
+
+	ptr = memalign(sz, sz);
+	if (!ptr) {
+		perror("memalign");
+		exit(1);
+	}
+	memset(ptr, 0xffffffff, sz);
+
+	for (i = 0; i < count; i++) {
+		fd = open(argv[1], O_CREAT|O_WRONLY);
+		if (fd < 0) {
+			perror(argv[1]);
+			exit(1);
+		}
+
+		done = 0;
+		while (!done) {
+			written = write(fd, ptr, sz);
+			if (written == -1) {
+				if (errno == ENOSPC) {
+					close(fd);
+					unlink(argv[1]);
+					printf("Unlinked %s\n", argv[1]);
+					done = 1;
+				}
+				else {
+					printf("Skipped unlink %s (%s)\n",
+						argv[1], strerror(errno));
+					done = -1;
+				}
+			}
+			if (written == 0) {
+				printf("Wrote zero bytes?\n");
+				done = -1;
+			}
+			bytes += written;
+		}
+		if (done > 0)
+			printf("Wrote %llu bytes total.\n", bytes);
+		else
+			exit(1);
+	}
+	printf("Completed %u iterations of unlink/out-of-space test.\n", i);
+	exit(0);
+}