src: fix up mmap() error checking

I noticed that in some of my C tests in src/ I was incorrectly
checking for mmap() failure by looking for NULL instead of
MAP_FAILED.  Fix those and clean up some places where we were
testing against -1 (the actual value of MAP_FAILED) which was
manually being cast to a pointer.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

src/aio-dio-regress/aio-io-setup-with-nonwritable-context-pointer.c

@@ -40,7 +40,7 @@ main(int __attribute__((unused)) argc, char **argv)
 	void *addr;
 
 	addr = mmap(NULL, 4096, PROT_READ, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
-	if (!addr) {
+	if (addr == MAP_FAILED) {
 		perror("mmap");
 		exit(1);
 	}

src/fstest.c

@@ -138,7 +138,7 @@ bozo!
 			exit(1);
 		}
 		p = mmap(NULL, file_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
-		if (p == (char *)-1) {
+		if (p == MAP_FAILED) {
 			perror("mmap");
 			exit(1);
 		}

src/t_ext4_dax_inline_corruption.c

@@ -37,14 +37,14 @@ int main(int argc, char *argv[])
 		err_exit("fd");
 
 	data = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
-	if (!data)
+	if (data == MAP_FAILED)
 		err_exit("mmap data");
 
 	/* this fallocate turns off inline data and turns on DAX */
 	fallocate(fd, 0, 0, PAGE(2));
 
 	dax_data = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
-	if (!dax_data)
+	if (dax_data == MAP_FAILED)
 		err_exit("mmap dax_data");
 
 	/*

src/t_ext4_dax_journal_corruption.c

@@ -60,7 +60,7 @@ int main(int argc, char *argv[])
 	fallocate(fd, 0, 0, len);
 
 	dax_data = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
-	if (!dax_data)
+	if (dax_data == MAP_FAILED)
 		err_exit("mmap dax_data");
 
 	/*
@@ -76,7 +76,7 @@ int main(int argc, char *argv[])
 	chattr_cmd(chattr, "+j", file);
 
 	data = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
-	if (!data)
+	if (data == MAP_FAILED)
 		err_exit("mmap data");
 
 	/*

src/t_mmap_stale_pmd.c

@@ -41,6 +41,8 @@ int main(int argc, char *argv[])
 	ftruncate(fd, MiB(4));
 
 	data = mmap(NULL, MiB(2), PROT_READ, MAP_SHARED, fd, MiB(2));
+	if (data == MAP_FAILED)
+		err_exit("mmap");
 
 	/*
 	 * This faults in a 2MiB zero page to satisfy the read.

src/t_mmap_writev.c

@@ -51,7 +51,7 @@ int main(int argc, char **argv)
 	if (fd==-1) {perror("open");exit(1);}
 
 	base = mmap(NULL,16384,PROT_READ,MAP_SHARED,fd,0);
-	if  (base == (void *)-1) { perror("mmap");exit(1); }
+	if  (base == MAP_FAILED) { perror("mmap");exit(1); }
 
 	unlink(new_file);