From 8b4ebef131656614386878692a07f8c51e533a8a Mon Sep 17 00:00:00 2001
From: Eric Wong <normalperson@yhbt.net>
Date: Sat, 9 May 2009 21:16:23 -0700
Subject: mincore: allow offset and length to be specified

Users won't have to mmap entire files if they don't want to
---
 mincore.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 53 insertions(+), 13 deletions(-)

diff --git a/mincore.c b/mincore.c
index 6b8b0e2..81a1262 100644
--- a/mincore.c
+++ b/mincore.c
@@ -1,12 +1,12 @@
 #include "compat-util.h"
 
-static void mincore_stats(const char *path)
+static void mincore_stats(const char *path, off_t offset, off_t len)
 {
-	struct stat sb;
 	char *map;
 	unsigned char *vec;
 	size_t vec_len;
 	size_t map_len;
+	off_t map_offset;
 	int fd;
 	size_t i;
 	static const char *fmt = sizeof(void *) == 8 ?
@@ -17,21 +17,29 @@ static void mincore_stats(const char *path)
 		return;
 	}
 
-	if (fstat(fd, &sb) < 0) {
-		fprintf(stderr, "%s: fstat(%d): %s\n",
-		        path, fd, strerror(errno));
-		goto err_close;
+	if (!len) {
+		struct stat sb;
+
+		if (fstat(fd, &sb) < 0) {
+			fprintf(stderr, "%s: fstat(%d): %s\n",
+				path, fd, strerror(errno));
+			goto err_close;
+		}
+		len = sb.st_size;
 	}
 
-	vec_len = (sb.st_size + page_size() - 1) / page_size();
+	vec_len = (len + page_size() - 1) / page_size();
 	if (!(vec = malloc(vec_len))) {
 		fprintf(stderr, "%s: malloc(%lu): %s\n",
 		        path, (unsigned long)vec_len, strerror(errno));
 		goto err_close;
 	}
 
-	map_len = PAGE_ALIGN(sb.st_size);
-	if (!(map = mmap(NULL, map_len, PROT_READ, MAP_SHARED, fd, 0))) {
+	map_len = PAGE_ALIGN(len);
+	map_offset = PAGE_ALIGN_DOWN(offset);
+
+	map = mmap(NULL, map_len, PROT_READ, MAP_SHARED, fd, map_offset);
+	if (!map) {
 		fprintf(stderr, "%s: mmap(%lu): %s\n",
 		        path, (unsigned long)vec_len, strerror(errno));
 		goto err_free;
@@ -44,7 +52,9 @@ static void mincore_stats(const char *path)
 	}
 
 	for (i = 0; i < vec_len; ++i)
-		printf(fmt, path, (unsigned long)(page_size() * i), vec[i]);
+		printf(fmt, path,
+		       (unsigned long)(page_size() * i) + map_offset,
+		       vec[i]);
 err_munmap:
 	munmap(map, map_len);
 err_free:
@@ -55,9 +65,39 @@ err_close:
 
 int main(int argc, char * const argv[])
 {
-	int i;
+	off_t offset = 0;
+	off_t len = 0;
+	int argi = 1;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "o:l:")) != -1) {
+		char *err;
+
+		argi += 2;
+		switch(opt) {
+		case 'o':
+			offset = strtol(optarg, &err, 10);
+			if (*err || offset < 0) {
+				fprintf(stderr, "offset must be >= 0\n");
+				return 1;
+			}
+			break;
+		case 'l':
+			len = strtol(optarg, &err, 10);
+			if (*err || len < 0) {
+				fprintf(stderr, "length must be >= 0\n");
+				return 1;
+			}
+			break;
+		default:
+			fprintf(stderr,
+			        "Usage: %s [-o offset] "
+				"[-l length] <files>\n", argv[0]);
+			return 1;
+		}
+	}
 
-	for (i = 1; i < argc; ++i)
-		mincore_stats(argv[i]);
+	for (; argi < argc; ++argi)
+		mincore_stats(argv[argi], offset, len);
 	return 0;
 }
-- 
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