usemem: add --offset option for mmap

usemem hardcodes 0 as the offset for mmap, so add an option to specify
this.  Use bytes for consistency with what mmap accepts.

How to parse the offset?  The POSIX standard is vague about off_t
("Signed integer type used for file sizes."), but in the absence of a
strtoofft, it seems reasonably safe to use strtol.  On 64-bit Arch and
Oracle Linux systems, off_t is the same size as long when compiling in
both 32-bit and 64-bit modes.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/usemem.c b/usemem.c
index 297f030..947a5aa 100644
--- a/usemem.c
+++ b/usemem.c
@@ -105,6 +105,7 @@ int map_shared = MAP_PRIVATE;
 int map_populate;
 int map_anonymous;
 int map_hugetlb;
+off_t map_offset;
 int fd;
 int start_ready_fds[2];
 int start_wake_fds[2];
@@ -121,6 +122,7 @@ void usage(int ok)
 	"    -b|--bind N         bind tasks with CPU number internal as N\n"
 	"    -a|--malloc         obtain memory from malloc()\n"
 	"    -f|--file FILE      mmap FILE, default /dev/zero\n"
+	"    -B|--offset bytes   mmap offset, default 0\n"
 	"    -F|--prefault       prefault mmap with MAP_POPULATE\n"
 	"    -P|--prealloc       allocate memory before fork\n"
 	"    -u|--unit SIZE      allocate memory in SIZE chunks\n"
@@ -173,6 +175,7 @@ static const struct option opts[] = {
 	{ "prefault"	, 0, NULL, 'F' },
 	{ "repeat"	, 1, NULL, 'r' },
 	{ "file"	, 1, NULL, 'f' },
+	{ "offset"	, 1, NULL, 'B' },
 	{ "pid-file"	, 1, NULL, 'p' },
 	{ "detach"	, 0, NULL, 'd' },
 	{ "sleep"	, 1, NULL, 's' },
@@ -390,7 +393,7 @@ unsigned long * allocate(unsigned long bytes)
 		p = mmap(NULL, bytes, (opt_readonly && !opt_openrw) ?
 			 PROT_READ : PROT_READ|PROT_WRITE,
 			 map_shared|map_populate|map_anonymous|map_hugetlb,
-			 map_anonymous ? -1 : fd, 0);
+			 map_anonymous ? -1 : fd, map_offset);
 		if (p == MAP_FAILED) {
 			fprintf(stderr, "%s: mmap failed: %s\n",
 				ourname, strerror(errno));
@@ -925,7 +928,7 @@ int main(int argc, char *argv[])
 	pagesize = getpagesize();
 
 	while ((c = getopt_long(argc, argv,
-				"aAf:FPp:gqowRMm:n:t:b:ds:T:Sr:u:j:e:EHDNLWyxOUh", opts, NULL)) != -1)
+				"aAB:f:FPp:gqowRMm:n:t:b:ds:T:Sr:u:j:e:EHDNLWyxOUh", opts, NULL)) != -1)
 		{
 		switch (c) {
 		case 'a':
@@ -944,6 +947,9 @@ int main(int argc, char *argv[])
 			filename = optarg;
 			map_shared = MAP_SHARED;
 			break;
+		case 'B':
+			map_offset = strtol(optarg, NULL, 10);
+			break;
 		case 'p':
 			pid_filename = optarg;
 			break;