Mmap in 512MB chunks

[overonion] / reverse_lib.c

diff --git a/reverse_lib.c b/reverse_lib.c
index 46563562f3b3833d44a67b0809e5887c2abb949e..f55bedf7b990458bee727df66f14a0961116beec 100644 (file)
--- a/reverse_lib.c
+++ b/reverse_lib.c
@@ -1,15 +1,24 @@
 #define _FILE_OFFSET_BITS 64
 
+#include "temp_file.h"
+
 #include <err.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sysexits.h>
 #include <unistd.h>
 
+static off_t ceil_div(off_t dividend, off_t divisor) {
+  return (dividend - 1) / divisor + 1;
+}
+
 void reverse_file(const char* input_filename, FILE* output_stream) {
+  const off_t mmap_chunk_size = 512 << 20;
+
   int fd = open(input_filename, O_RDONLY);
   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
 
@@ -17,15 +26,51 @@ void reverse_file(const char* input_filename, FILE* output_stream) {
   if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
 
   long page_size = sysconf(_SC_PAGE_SIZE);
-  off_t pages = (stats.st_size - 1) / page_size + 1;
-  long map_size = pages * page_size;
-  char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, 0);
-  if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap input");
+  off_t num_chunks = ceil_div(stats.st_size, mmap_chunk_size);
+  for (off_t chunk = num_chunks - 1; chunk >= 0; chunk--) {
+    off_t start_offset = chunk * mmap_chunk_size;
+    off_t end_offset = (chunk + 1) * mmap_chunk_size;
+    if (end_offset > stats.st_size) {
+      end_offset = stats.st_size;
+    }
+    off_t pages = ceil_div(end_offset - start_offset, page_size);
+    long map_size = pages * page_size;
+    char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, start_offset);
+    if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap chunk %lld of %lld", chunk, num_chunks);
 
-  for (off_t p = stats.st_size - 1; p >= 0; p--) {
-    if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
+    for (off_t p = (end_offset - start_offset) - 1; p >= 0; p--) {
+      if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
+    }
+
+    if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap chunk %lld of %lld", chunk, num_chunks);
   }
 
-  if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap input");
   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
 }
+
+/* Copy data from input to output until EOF is reached. */
+static void copy(FILE* input, FILE* output) {
+  for (;;) {
+    int c = fgetc(input);
+    if (c == EOF) {
+      if (ferror(input)) errx(EX_IOERR, "Could not read");
+      if (!feof(input)) errx(EX_IOERR, "Unexpected end of file");
+      break;
+    }
+    if (fputc(c, output) == EOF) errx(EX_IOERR, "Could not write");
+  }
+}
+
+void reverse_stream(FILE* input_stream, FILE* output_stream) {
+  char* temp_filename;
+  FILE* temp_file;
+  make_temporary_file(&temp_filename, &temp_file);
+
+  copy(input_stream, temp_file);
+  if (fclose(temp_file) != 0) err(EX_IOERR, "Could not close temporary file");
+
+  reverse_file(temp_filename, output_stream);
+
+  if (unlink(temp_filename) == -1) err(EX_IOERR, "Could not remove temporary file");
+  free(temp_filename);
+}