All of lore.kernel.org
 help / color / mirror / Atom feed
From: Eric Wong <e@80x24.org>
To: Eric Sunshine <sunshine@sunshineco.com>
Cc: git@vger.kernel.org
Subject: [PATCH v2] update-server-info: avoid needless overwrites
Date: Sat, 11 May 2019 20:47:54 +0000	[thread overview]
Message-ID: <20190511204754.quj52fbwrdqxg6e7@dcvr> (raw)
In-Reply-To: <CAPig+cRZy4yM+ZuHhZK3tPV_QRvSy63aHBZZj6AcFTu+5FNG0A@mail.gmail.com>

Eric Sunshine <sunshine@sunshineco.com> wrote:
> On Fri, May 10, 2019 at 9:35 PM Eric Wong <e@80x24.org> wrote:
> > +       if (strbuf_fread(&tmp, (size_t)new_len, fp) != (size_t)new_len)
> > +               return 1;
> 
> Although strbuf_fread() will release 'tmp' automatically if the read
> actually fails, it won't do so otherwise. So, if it reads more or
> fewer bytes than expected, for some reason, then this early return
> will leak the strbuf, won't it?

> > +       if (strbuf_read_file(&tmp, path, (size_t)st.st_size) < 0)
> > +               return 1;
> 
> Same issue.
> 
> > diff --git a/t/t5200-update-server-info.sh b/t/t5200-update-server-info.sh
> > @@ -0,0 +1,41 @@
> > +test_description='Test git stash show configuration.'
> 
> Copy/paste error for test description?

Yup, thanks for the review.  Updated patch below

-----8<------
Subject: [PATCH] update-server-info: avoid needless overwrites

Do not change the existing info/refs and objects/info/packs
files if they match the existing content on the filesystem.
This is intended to preserve mtime and make it easier for dumb
HTTP pollers to rely on the If-Modified-Since header.

Combined with stdio and kernel buffering; the kernel should be
able to avoid block layer writes and reduce wear.

Signed-off-by: Eric Wong <e@80x24.org>
---
Interdiff:
  diff --git a/server-info.c b/server-info.c
  index 34599e4817..11515804d4 100644
  --- a/server-info.c
  +++ b/server-info.c
  @@ -24,15 +24,19 @@ static int files_differ(FILE *fp, const char *path)
   		return 1;
   
   	rewind(fp);
  -	if (strbuf_fread(&tmp, (size_t)new_len, fp) != (size_t)new_len)
  +	if (strbuf_fread(&tmp, (size_t)new_len, fp) != (size_t)new_len) {
  +		strbuf_release(&tmp);
   		return 1;
  +	}
   	the_hash_algo->init_fn(&c);
   	the_hash_algo->update_fn(&c, tmp.buf, tmp.len);
   	the_hash_algo->final_fn(oid_new.hash, &c);
   	strbuf_release(&tmp);
   
  -	if (strbuf_read_file(&tmp, path, (size_t)st.st_size) < 0)
  +	if (strbuf_read_file(&tmp, path, (size_t)st.st_size) < 0) {
  +		strbuf_release(&tmp);
   		return 1;
  +	}
   	the_hash_algo->init_fn(&c);
   	the_hash_algo->update_fn(&c, tmp.buf, tmp.len);
   	the_hash_algo->final_fn(oid_old.hash, &c);
  diff --git a/t/t5200-update-server-info.sh b/t/t5200-update-server-info.sh
  index f1cec46914..21a58eecb9 100755
  --- a/t/t5200-update-server-info.sh
  +++ b/t/t5200-update-server-info.sh
  @@ -1,6 +1,6 @@
   #!/bin/sh
   
  -test_description='Test git stash show configuration.'
  +test_description='Test git update-server-info'
   
   . ./test-lib.sh
   

 server-info.c                 | 65 +++++++++++++++++++++++++++++------
 t/t5200-update-server-info.sh | 41 ++++++++++++++++++++++
 2 files changed, 96 insertions(+), 10 deletions(-)
 create mode 100755 t/t5200-update-server-info.sh

diff --git a/server-info.c b/server-info.c
index 41274d098b..11515804d4 100644
--- a/server-info.c
+++ b/server-info.c
@@ -6,37 +6,82 @@
 #include "tag.h"
 #include "packfile.h"
 #include "object-store.h"
+#include "strbuf.h"
+
+static int files_differ(FILE *fp, const char *path)
+{
+	struct stat st;
+	git_hash_ctx c;
+	struct object_id oid_old, oid_new;
+	struct strbuf tmp = STRBUF_INIT;
+	long new_len = ftell(fp);
+
+	if (new_len < 0 || stat(path, &st) < 0)
+		return 1;
+	if (!S_ISREG(st.st_mode))
+		return 1;
+	if ((off_t)new_len != st.st_size)
+		return 1;
+
+	rewind(fp);
+	if (strbuf_fread(&tmp, (size_t)new_len, fp) != (size_t)new_len) {
+		strbuf_release(&tmp);
+		return 1;
+	}
+	the_hash_algo->init_fn(&c);
+	the_hash_algo->update_fn(&c, tmp.buf, tmp.len);
+	the_hash_algo->final_fn(oid_new.hash, &c);
+	strbuf_release(&tmp);
+
+	if (strbuf_read_file(&tmp, path, (size_t)st.st_size) < 0) {
+		strbuf_release(&tmp);
+		return 1;
+	}
+	the_hash_algo->init_fn(&c);
+	the_hash_algo->update_fn(&c, tmp.buf, tmp.len);
+	the_hash_algo->final_fn(oid_old.hash, &c);
+	strbuf_release(&tmp);
+
+	return hashcmp(oid_old.hash, oid_new.hash);
+}
 
 /*
  * Create the file "path" by writing to a temporary file and renaming
  * it into place. The contents of the file come from "generate", which
  * should return non-zero if it encounters an error.
  */
-static int update_info_file(char *path, int (*generate)(FILE *))
+static int update_info_file(char *path, int (*generate)(FILE *), int force)
 {
 	char *tmp = mkpathdup("%s_XXXXXX", path);
 	int ret = -1;
 	int fd = -1;
 	FILE *fp = NULL, *to_close;
+	int do_update;
 
 	safe_create_leading_directories(path);
 	fd = git_mkstemp_mode(tmp, 0666);
 	if (fd < 0)
 		goto out;
-	to_close = fp = fdopen(fd, "w");
+	to_close = fp = fdopen(fd, "w+");
 	if (!fp)
 		goto out;
 	fd = -1;
 	ret = generate(fp);
 	if (ret)
 		goto out;
+
+	do_update = force || files_differ(fp, path);
 	fp = NULL;
 	if (fclose(to_close))
 		goto out;
-	if (adjust_shared_perm(tmp) < 0)
-		goto out;
-	if (rename(tmp, path) < 0)
-		goto out;
+	if (do_update) {
+		if (adjust_shared_perm(tmp) < 0)
+			goto out;
+		if (rename(tmp, path) < 0)
+			goto out;
+	} else {
+		unlink(tmp);
+	}
 	ret = 0;
 
 out:
@@ -78,10 +123,10 @@ static int generate_info_refs(FILE *fp)
 	return for_each_ref(add_info_ref, fp);
 }
 
-static int update_info_refs(void)
+static int update_info_refs(int force)
 {
 	char *path = git_pathdup("info/refs");
-	int ret = update_info_file(path, generate_info_refs);
+	int ret = update_info_file(path, generate_info_refs, force);
 	free(path);
 	return ret;
 }
@@ -254,7 +299,7 @@ static int update_info_packs(int force)
 	int ret;
 
 	init_pack_info(infofile, force);
-	ret = update_info_file(infofile, write_pack_info_file);
+	ret = update_info_file(infofile, write_pack_info_file, force);
 	free_pack_info();
 	free(infofile);
 	return ret;
@@ -269,7 +314,7 @@ int update_server_info(int force)
 	 */
 	int errs = 0;
 
-	errs = errs | update_info_refs();
+	errs = errs | update_info_refs(force);
 	errs = errs | update_info_packs(force);
 
 	/* remove leftover rev-cache file if there is any */
diff --git a/t/t5200-update-server-info.sh b/t/t5200-update-server-info.sh
new file mode 100755
index 0000000000..21a58eecb9
--- /dev/null
+++ b/t/t5200-update-server-info.sh
@@ -0,0 +1,41 @@
+#!/bin/sh
+
+test_description='Test git update-server-info'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' 'test_commit file'
+
+test_expect_success 'create info/refs' '
+	git update-server-info &&
+	test_path_is_file .git/info/refs
+'
+
+test_expect_success 'modify and store mtime' '
+	test-tool chmtime =0 .git/info/refs &&
+	test-tool chmtime --get .git/info/refs >a
+'
+
+test_expect_success 'info/refs is not needlessly overwritten' '
+	git update-server-info &&
+	test-tool chmtime --get .git/info/refs >b &&
+	test_cmp a b
+'
+
+test_expect_success 'info/refs can be forced to update' '
+	git update-server-info -f &&
+	test-tool chmtime --get .git/info/refs >b &&
+	! test_cmp a b
+'
+
+test_expect_success 'info/refs updates when changes are made' '
+	test-tool chmtime =0 .git/info/refs &&
+	test-tool chmtime --get .git/info/refs >b &&
+	test_cmp a b &&
+	git update-ref refs/heads/foo HEAD &&
+	git update-server-info &&
+	test-tool chmtime --get .git/info/refs >b &&
+	! test_cmp a b
+'
+
+test_done
-- 
EW

  reply	other threads:[~2019-05-11 20:47 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-11  1:34 [PATCH] update-server-info: avoid needless overwrites Eric Wong
2019-05-11  7:35 ` Eric Sunshine
2019-05-11 20:47   ` Eric Wong [this message]
2019-05-11 21:17 ` Eric Wong
2019-05-11 23:37 ` Ævar Arnfjörð Bjarmason
2019-05-12  0:38   ` Eric Wong
2019-05-12  4:08   ` Jeff King
2019-05-12  7:16     ` Ævar Arnfjörð Bjarmason
2019-05-14  9:47       ` Jeff King
2019-05-14 10:33         ` Ævar Arnfjörð Bjarmason
2019-05-14 11:24           ` Jeff King
2019-05-14 11:57             ` Ævar Arnfjörð Bjarmason
2019-05-14 11:50         ` Eric Wong
2019-05-14 12:13           ` dumb HTTP things I want to do Eric Wong
2019-05-14 12:27             ` Jeff King
2019-05-14 12:19           ` [PATCH] update-server-info: avoid needless overwrites Ævar Arnfjörð Bjarmason
2019-05-14 12:29             ` Jeff King
2019-05-15  0:45             ` [PATCH 2/1] server-info: conditionally update on fetch Eric Wong
2019-05-15 20:38               ` [WIP] repack leaving stale entries in objects/info/packs Eric Wong
2019-05-15 21:48                 ` Jeff King
2019-05-23  8:59                   ` [PATCH] server-info: do not list unlinked packs Eric Wong
2019-05-23 10:24                     ` Jeff King
2019-05-23 17:27                       ` [PATCH v2] " Eric Wong
2019-05-24  6:05                         ` Jeff King
2019-05-24  7:34                         ` Ævar Arnfjörð Bjarmason
2019-05-13 23:17 ` [PATCH v3] update-server-info: avoid needless overwrites Eric Wong

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190511204754.quj52fbwrdqxg6e7@dcvr \
    --to=e@80x24.org \
    --cc=git@vger.kernel.org \
    --cc=sunshine@sunshineco.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.