gvfs: add the feature to skip writing the index' SHA-1

This takes a substantial amount of time, and if the user is reasonably
sure that the files' integrity is not compromised, that time can be saved.

Git no longer verifies the SHA-1 by default, anyway.

Signed-off-by: Kevin Willford <kewillf@microsoft.com>

Documentation/config/core.txt

@@ -729,7 +729,15 @@ core.multiPackIndex::
 	information. Defaults to true.
 
 core.gvfs::
-	Enable the features needed for GVFS.
+	Enable the features needed for GVFS.  This value can be set to true
+	to indicate all features should be turned on or the bit values listed
+	below can be used to turn on specific features.
++
+--
+	GVFS_SKIP_SHA_ON_INDEX::
+		Bit value 1
+		Disables the calculation of the sha when writing the index
+--
 
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]

csum-file.c

@@ -45,7 +45,8 @@ void hashflush(struct hashfile *f)
 	unsigned offset = f->offset;
 
 	if (offset) {
-		the_hash_algo->update_fn(&f->ctx, f->buffer, offset);
+		if (!f->skip_hash)
+			the_hash_algo->update_fn(&f->ctx, f->buffer, offset);
 		flush(f, f->buffer, offset);
 		f->offset = 0;
 	}
@@ -64,7 +65,16 @@ int finalize_hashfile(struct hashfile *f, unsigned char *result,
 	int fd;
 
 	hashflush(f);
-	the_hash_algo->final_fn(f->buffer, &f->ctx);
+
+	/*
+	 * If we skip the hash function, be sure to create an empty hash
+	 * for the results.
+	 */
+	if (f->skip_hash)
+		memset(f->buffer, 0, the_hash_algo->rawsz);
+	else
+		the_hash_algo->final_fn(f->buffer, &f->ctx);
+
 	if (result)
 		hashcpy(result, f->buffer);
 	if (flags & CSUM_HASH_IN_STREAM)
@@ -158,6 +168,7 @@ static struct hashfile *hashfd_internal(int fd, const char *name,
 	f->buffer_len = buffer_len;
 	f->buffer = xmalloc(buffer_len);
 	f->check_buffer = NULL;
+	f->skip_hash = 0;
 
 	return f;
 }

csum-file.h

@@ -20,6 +20,13 @@ struct hashfile {
 	size_t buffer_len;
 	unsigned char *buffer;
 	unsigned char *check_buffer;
+
+	/*
+	 * If set to 1, skip_hash indicates that we should
+	 * not actually compute the hash for this hashfile and
+	 * instead only use it as a buffered write.
+	 */
+	int skip_hash;
 };
 
 /* Checkpoint */

gvfs.h

@@ -9,6 +9,12 @@
  * used for GVFS functionality
  */
 
+
+/*
+ * The list of bits in the core_gvfs setting
+ */
+#define GVFS_SKIP_SHA_ON_INDEX                      (1 << 0)
+
 static inline int gvfs_config_is_set(int mask) {
 	return (core_gvfs & mask) == mask;
 }

read-cache.c

@@ -4,6 +4,7 @@
  * Copyright (C) Linus Torvalds, 2005
  */
 #include "cache.h"
+#include "gvfs.h"
 #include "config.h"
 #include "diff.h"
 #include "diffcore.h"
@@ -2910,6 +2911,9 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 
 	f = hashfd(tempfile->fd, tempfile->filename.buf);
 
+	if (gvfs_config_is_set(GVFS_SKIP_SHA_ON_INDEX))
+		f->skip_hash = 1;
+
 	for (i = removed = extended = 0; i < entries; i++) {
 		if (cache[i]->ce_flags & CE_REMOVE)
 			removed++;

t/t1016-read-tree-skip-sha-on-read.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+test_description='check that read-tree works with core.gvfs config value'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-read-tree.sh
+
+test_expect_success setup '
+	echo one >a &&
+	git add a &&
+	git commit -m initial
+'
+test_expect_success 'read-tree without core.gvsf' '
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_expect_success 'read-tree with core.gvfs set to 1' '
+	git config core.gvfs 1 &&
+	read_tree_u_must_succeed -m -u HEAD
+'
+
+test_done