Yank writing-back support from gitfakemmap.

We do not write through our use of mmap(), so make sure callers pass
MAP_PRIVATE and remove support for writing changes back.

Signed-off-by: Junio C Hamano <junkio@cox.net>

compat/mmap.c

@@ -4,43 +4,33 @@
 #include <errno.h>
 #include "../cache.h"
 
-typedef struct fakemmapwritable {
-	void *start;
-	size_t length;
-	int fd;
-	off_t offset;
-	struct fakemmapwritable *next;
-} fakemmapwritable;
-
-static fakemmapwritable *writablelist = NULL;
-
 void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_t offset)
 {
 	int n = 0;
 
-	if(start != NULL)
+	if (start != NULL || !(flags & MAP_PRIVATE))
 		die("Invalid usage of gitfakemmap.");
 
-	if(lseek(fd, offset, SEEK_SET)<0) {
+	if (lseek(fd, offset, SEEK_SET) < 0) {
 		errno = EINVAL;
 		return MAP_FAILED;
 	}
 
 	start = xmalloc(length);
-	if(start == NULL) {
+	if (start == NULL) {
 		errno = ENOMEM;
 		return MAP_FAILED;
 	}
 
-	while(n < length) {
+	while (n < length) {
 		int count = read(fd, start+n, length-n);
 
-		if(count == 0) {
+		if (count == 0) {
 			memset(start+n, 0, length-n);
 			break;
 		}
 
-		if(count < 0) {
+		if (count < 0) {
 			free(start);
 			errno = EACCES;
 			return MAP_FAILED;
@@ -49,65 +39,12 @@ void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_
 		n += count;
 	}
 
-	if(prot & PROT_WRITE) {
-		fakemmapwritable *next = xmalloc(sizeof(fakemmapwritable));
-		next->start = start;
-		next->length = length;
-		next->fd = dup(fd);
-		next->offset = offset;
-		next->next = writablelist;
-		writablelist = next;
-	}
-
 	return start;
 }
 
 int gitfakemunmap(void *start, size_t length)
 {
-	fakemmapwritable *writable = writablelist, *before = NULL;
-
-	while(writable && (writable->start > start + length
-			|| writable->start + writable->length < start)) {
-		before = writable;
-		writable = writable->next;
-	}
-
-	if(writable) {
-		/* need to write back the contents */
-		int n = 0;
-
-		if(writable->start != start || writable->length != length)
-			die("fakemmap does not support partial write back.");
-
-		if(lseek(writable->fd, writable->offset, SEEK_SET) < 0) {
-			free(start);
-			errno = EBADF;
-			return -1;
-		}
-
-		while(n < length) {
-			int count = write(writable->fd, start + n, length - n);
-
-			if(count < 0) {
-				errno = EINVAL;
-				return -1;
-			}
-
-			n += count;
-		}
-
-		close(writable->fd);
-
-		if(before)
-			before->next = writable->next;
-		else
-			writablelist = writable->next;
-
-		free(writable);
-	}
-
 	free(start);
-
 	return 0;
 }