Only malloc the buffer for fast file copy when needed

kitty/data-types.h

@@ -368,5 +368,4 @@ void play_canberra_sound(const char *which_sound, const char *event_id, bool is_
 SPRITE_MAP_HANDLE alloc_sprite_map(unsigned int, unsigned int);
 SPRITE_MAP_HANDLE free_sprite_map(SPRITE_MAP_HANDLE);
 const char* get_hyperlink_for_id(const HYPERLINK_POOL_HANDLE, hyperlink_id_type id, bool only_url);
-bool copy_between_files(int infd, int outfd, off_t in_pos, size_t len, uint8_t *buf, size_t bufsz);
 void log_event(const char *format, ...) __attribute__((format(printf, 1, 2)));

kitty/disk-cache.c

@@ -11,6 +11,7 @@
 #include "safe-wrappers.h"
 #include "kitty-uthash.h"
 #include "loop-utils.h"
+#include "fast-file-copy.h"
 #include "threading.h"
 #include "cross-platform-random.h"
 #include <structmember.h>
@@ -132,8 +133,7 @@ static void
 defrag(DiskCache *self) {
     int new_cache_file = -1;
     FREE_AFTER_FUNCTION DefragEntry *defrag_entries = NULL;
-    FREE_AFTER_FUNCTION uint8_t *buf = NULL;
-    const size_t bufsz = 1024 * 1024;
+    AutoFreeFastFileCopyBuffer fcb = {0};
     bool lock_released = false, ok = false;
 
     off_t size_on_disk = size_of_cache_file(self);
@@ -164,17 +164,13 @@ defrag(DiskCache *self) {
         goto cleanup;
     }
     lseek(new_cache_file, 0, SEEK_SET);
-#ifndef HAS_SENDFILE
-    buf = malloc(bufsz);
-    if (!buf) goto cleanup;
-#endif
 
     mutex(unlock); lock_released = true;
 
     off_t current_pos = 0;
     for (size_t i = 0; i < num_entries_to_defrag; i++) {
         DefragEntry *e = defrag_entries + i;
-        if (!copy_between_files(self->cache_file_fd, new_cache_file, e->old_offset, e->data_sz, buf, bufsz)) {
+        if (!copy_between_files(self->cache_file_fd, new_cache_file, e->old_offset, e->data_sz, &fcb)) {
             perror("Failed to copy data to new disk cache file during defrag");
             goto cleanup;
         }

kitty/fast-file-copy.c

@@ -5,19 +5,15 @@
  * Distributed under terms of the GPL3 license.
  */
 
-#include "data-types.h"
+#include "fast-file-copy.h"
 #if __linux__
 #define HAS_SENDFILE
-#endif
-
-#ifdef HAS_SENDFILE
 #include <sys/sendfile.h>
 #endif
 
-bool
-copy_between_files(int infd, int outfd, off_t in_pos, size_t len, uint8_t *buf, size_t bufsz) {
 #ifdef HAS_SENDFILE
-    (void)buf; (void)bufsz;
+static bool
+copy_with_sendfile(int infd, int outfd, off_t in_pos, size_t len) {
     unsigned num_of_consecutive_zero_returns = 128;
     while (len) {
         off_t r = in_pos;
@@ -34,9 +30,19 @@ copy_between_files(int infd, int outfd, off_t in_pos, size_t len, uint8_t *buf,
         num_of_consecutive_zero_returns = 128;
         in_pos += n; len -= n;
     }
-#else
+    return true;
+}
+#endif
+
+static inline bool
+copy_with_buffer(int infd, int outfd, off_t in_pos, size_t len, FastFileCopyBuffer *fcb) {
+    if (!fcb->buf) {
+        fcb->sz = 16 * 1024;
+        fcb->buf = malloc(fcb->sz);
+        if (!fcb->buf) return false;
+    }
     while (len) {
-        ssize_t amt_read = pread(infd, buf, MIN(len, bufsz), in_pos);
+        ssize_t amt_read = pread(infd, fcb->buf, MIN(len, fcb->sz), in_pos);
         if (amt_read < 0) {
             if (errno == EINTR || errno == EAGAIN) continue;
             return false;
@@ -47,7 +53,7 @@ copy_between_files(int infd, int outfd, off_t in_pos, size_t len, uint8_t *buf,
         }
         len -= amt_read;
         in_pos += amt_read;
-        uint8_t *p = buf;
+        uint8_t *p = fcb->buf;
         while(amt_read) {
             ssize_t amt_written = write(outfd, p, amt_read);
             if (amt_written < 0) {
@@ -62,6 +68,17 @@ copy_between_files(int infd, int outfd, off_t in_pos, size_t len, uint8_t *buf,
             p += amt_written;
         }
     }
+    return true;
+#undef bufsz
+}
+
+bool
+copy_between_files(int infd, int outfd, off_t in_pos, size_t len, FastFileCopyBuffer *fcb) {
+#ifdef HAS_SENDFILE
+    (void)fcb;
+    return copy_with_sendfile(infd, outfd, in_pos, len);
+#else
+    return copy_with_buffer(infd, outfd, in_pos, len, fcb);
 #endif
     return true;
 }

kitty/fast-file-copy.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2021 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#pragma once
+
+#include "data-types.h"
+
+typedef struct FastFileCopyBuffer {
+    uint8_t *buf;
+    size_t sz;
+} FastFileCopyBuffer;
+
+static inline void
+free_fast_file_copy_buffer(FastFileCopyBuffer *fcb) { free(fcb->buf); }
+
+#define FREE_FCB_AFTER_FUNCTION __attribute__ ((__cleanup__(free_fast_file_copy_buffer)))
+#define AutoFreeFastFileCopyBuffer FREE_FCB_AFTER_FUNCTION FastFileCopyBuffer
+
+bool copy_between_files(int infd, int outfd, off_t in_pos, size_t len, FastFileCopyBuffer *fcb);