[PATCH] If NO_MMAP is defined, fake mmap() and munmap()

Since some platforms do not support mmap() at all, and others do only just
so, this patch introduces the option to fake mmap() and munmap() by
malloc()ing and read()ing explicitely.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>

4 files changed, 135 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 1bdf4de75d..7ca77cf2af 100644
--- a/Makefile
+++ b/Makefile
@@ -27,6 +27,8 @@
 # Define NEEDS_SOCKET if linking with libc is not enough (SunOS,
 # Patrick Mauritz).
 #
+# Define NO_MMAP if you want to avoid mmap.
+#
 # Define WITH_OWN_SUBPROCESS_PY if you want to use with python 2.3.
 #
 # Define NO_IPV6 if you lack IPv6 support and getaddrinfo().
@@ -258,6 +260,10 @@ ifdef NO_STRCASESTR
 	DEFINES += -Dstrcasestr=gitstrcasestr
 	LIB_OBJS += compat/strcasestr.o
 endif
+ifdef NO_MMAP
+	DEFINES += -Dmmap=gitfakemmap -Dmunmap=gitfakemunmap -DNO_MMAP
+	LIB_OBJS += compat/mmap.o
+endif
 ifdef NO_IPV6
 	DEFINES += -DNO_IPV6 -Dsockaddr_storage=sockaddr_in
 endif
diff --git a/cache.h b/cache.h
index 514adb8f8e..5987d4c125 100644
--- a/cache.h
+++ b/cache.h
@@ -11,7 +11,9 @@
 #include <string.h>
 #include <errno.h>
 #include <limits.h>
+#ifndef NO_MMAP
 #include <sys/mman.h>
+#endif
 #include <sys/param.h>
 #include <netinet/in.h>
 #include <sys/types.h>
@@ -356,4 +358,18 @@ extern void packed_object_info_detail(struct pack_entry *, char *, unsigned long
 /* Dumb servers support */
 extern int update_server_info(int);
 
+#ifdef NO_MMAP
+
+#ifndef PROT_READ
+#define PROT_READ 1
+#define PROT_WRITE 2
+#define MAP_PRIVATE 1
+#define MAP_FAILED ((void*)-1)
+#endif
+
+extern void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_t offset);
+extern int gitfakemunmap(void *start, size_t length);
+
+#endif
+
 #endif /* CACHE_H */
diff --git a/compat/mmap.c b/compat/mmap.c
new file mode 100644
index 0000000000..fca6321ce0
--- /dev/null
+++ b/compat/mmap.c
@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#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)
+		die("Invalid usage of gitfakemmap.");
+
+	if(lseek(fd, offset, SEEK_SET)<0) {
+		errno = EINVAL;
+		return MAP_FAILED;
+	}
+
+	start = xmalloc(length);
+	if(start == NULL) {
+		errno = ENOMEM;
+		return MAP_FAILED;
+	}
+
+	while(n < length) {
+		int count = read(fd, start+n, length-n);
+
+		if(count == 0) {
+			memset(start+n, 0, length-n);
+			break;
+		}
+
+		if(count < 0) {
+			free(start);
+			errno = EACCES;
+			return MAP_FAILED;
+		}
+
+		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;
+}
+
diff --git a/mailsplit.c b/mailsplit.c
index 7981f87a72..0f8100dcca 100644
--- a/mailsplit.c
+++ b/mailsplit.c
@@ -9,7 +9,6 @@
 #include <fcntl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#include <sys/mman.h>
 #include <string.h>
 #include <stdio.h>
 #include <ctype.h>