diff mbox series

[v3,2/5] fetch: use strbuf to format FETCH_HEAD updates

Message ID a19762690eb7f9957ac31d73e110f0103aeb2307.1610362744.git.ps@pks.im (mailing list archive)
State New, archived
Headers show
Series fetch: implement support for atomic reference updates | expand

Commit Message

Patrick Steinhardt Jan. 11, 2021, 11:05 a.m. UTC 
This commit refactors `append_fetch_head()` to use a `struct strbuf` for
formatting the update which we're about to append to the FETCH_HEAD
file. While the refactoring doesn't have much of a benefit right now, it
servers as a preparatory step to implement atomic fetches where we need
to buffer all updates to FETCH_HEAD and only flush them out if all
reference updates succeeded.

No change in behaviour is expected from this commit.
---
 builtin/fetch.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

Comments

Patrick Steinhardt Jan. 11, 2021, 11:10 a.m. UTC | #1 
On Mon, Jan 11, 2021 at 12:05:20PM +0100, Patrick Steinhardt wrote:
> This commit refactors `append_fetch_head()` to use a `struct strbuf` for
> formatting the update which we're about to append to the FETCH_HEAD
> file. While the refactoring doesn't have much of a benefit right now, it
> servers as a preparatory step to implement atomic fetches where we need
> to buffer all updates to FETCH_HEAD and only flush them out if all
> reference updates succeeded.
> 
> No change in behaviour is expected from this commit.

Forgot to add my

Signed-off-by: Patrick Steinhardt <ps@pks.im>

Will amend in v4.

Patrick

> ---
>  builtin/fetch.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 50f0306a92..1252f37493 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -899,6 +899,7 @@ static int iterate_ref_map(void *cb_data, struct object_id *oid)
>  
>  struct fetch_head {
>  	FILE *fp;
> +	struct strbuf buf;
>  };
>  
>  static int open_fetch_head(struct fetch_head *fetch_head)
> @@ -909,6 +910,7 @@ static int open_fetch_head(struct fetch_head *fetch_head)
>  		fetch_head->fp = fopen(filename, "a");
>  		if (!fetch_head->fp)
>  			return error_errno(_("cannot open %s"), filename);
> +		strbuf_init(&fetch_head->buf, 0);
>  	} else {
>  		fetch_head->fp = NULL;
>  	}
> @@ -941,14 +943,17 @@ static void append_fetch_head(struct fetch_head *fetch_head,
>  			return;
>  	}
>  
> -	fprintf(fetch_head->fp, "%s\t%s\t%s",
> -		oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
> +	strbuf_addf(&fetch_head->buf, "%s\t%s\t%s",
> +		    oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
>  	for (i = 0; i < url_len; ++i)
>  		if ('\n' == url[i])
> -			fputs("\\n", fetch_head->fp);
> +			strbuf_addstr(&fetch_head->buf, "\\n");
>  		else
> -			fputc(url[i], fetch_head->fp);
> -	fputc('\n', fetch_head->fp);
> +			strbuf_addch(&fetch_head->buf, url[i]);
> +	strbuf_addch(&fetch_head->buf, '\n');
> +
> +	strbuf_write(&fetch_head->buf, fetch_head->fp);
> +	strbuf_reset(&fetch_head->buf);
>  }
>  
>  static void commit_fetch_head(struct fetch_head *fetch_head)
> @@ -962,6 +967,7 @@ static void close_fetch_head(struct fetch_head *fetch_head)
>  		return;
>  
>  	fclose(fetch_head->fp);
> +	strbuf_release(&fetch_head->buf);
>  }
>  
>  static const char warn_show_forced_updates[] =
> -- 
> 2.30.0
>
Christian Couder Jan. 11, 2021, 11:17 a.m. UTC | #2 
On Mon, Jan 11, 2021 at 12:05 PM Patrick Steinhardt <ps@pks.im> wrote:
>
> This commit refactors `append_fetch_head()` to use a `struct strbuf` for
> formatting the update which we're about to append to the FETCH_HEAD
> file. While the refactoring doesn't have much of a benefit right now, it
> servers as a preparatory step to implement atomic fetches where we need

s/servers/serves/

> to buffer all updates to FETCH_HEAD and only flush them out if all
> reference updates succeeded.
Junio C Hamano Jan. 11, 2021, 11:21 p.m. UTC | #3 
Patrick Steinhardt <ps@pks.im> writes:

> @@ -909,6 +910,7 @@ static int open_fetch_head(struct fetch_head *fetch_head)
>  		fetch_head->fp = fopen(filename, "a");
>  		if (!fetch_head->fp)
>  			return error_errno(_("cannot open %s"), filename);
> +		strbuf_init(&fetch_head->buf, 0);
>  	} else {
>  		fetch_head->fp = NULL;
>  	}

Leaving fetch_head->buf uninitialized is probably OK as the caller
of open_fetch_head() would (or at least should) immediately barf
upon seeing an error return?

Ah, no.  Under dry-run mode, we will return success but leave buf
uninitializesd.  It is safe because we do not use the strbuf when fp
is NULL.  OK.

> @@ -941,14 +943,17 @@ static void append_fetch_head(struct fetch_head *fetch_head,
>  			return;
>  	}
>  
> -	fprintf(fetch_head->fp, "%s\t%s\t%s",
> -		oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
> +	strbuf_addf(&fetch_head->buf, "%s\t%s\t%s",
> +		    oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
>  	for (i = 0; i < url_len; ++i)
>  		if ('\n' == url[i])
> -			fputs("\\n", fetch_head->fp);
> +			strbuf_addstr(&fetch_head->buf, "\\n");
>  		else
> -			fputc(url[i], fetch_head->fp);
> -	fputc('\n', fetch_head->fp);
> +			strbuf_addch(&fetch_head->buf, url[i]);
> +	strbuf_addch(&fetch_head->buf, '\n');
> +
> +	strbuf_write(&fetch_head->buf, fetch_head->fp);
> +	strbuf_reset(&fetch_head->buf);

This gets us closer to fixing the "one record can be written out
with multiple write(2) calls, allowing parallel fetches to corrupt
FETCH_HEAD file by intermixed records" problem (even though this
change alone would not solve it---for that we need to do write
ourselves, not letting stdio do the flushing).

>  }
>  
>  static void commit_fetch_head(struct fetch_head *fetch_head)
> @@ -962,6 +967,7 @@ static void close_fetch_head(struct fetch_head *fetch_head)
>  		return;
>  
>  	fclose(fetch_head->fp);
> +	strbuf_release(&fetch_head->buf);
>  }
>  
>  static const char warn_show_forced_updates[] =
diff mbox series

Patch

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 50f0306a92..1252f37493 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -899,6 +899,7 @@  static int iterate_ref_map(void *cb_data, struct object_id *oid)
 
 struct fetch_head {
 	FILE *fp;
+	struct strbuf buf;
 };
 
 static int open_fetch_head(struct fetch_head *fetch_head)
@@ -909,6 +910,7 @@  static int open_fetch_head(struct fetch_head *fetch_head)
 		fetch_head->fp = fopen(filename, "a");
 		if (!fetch_head->fp)
 			return error_errno(_("cannot open %s"), filename);
+		strbuf_init(&fetch_head->buf, 0);
 	} else {
 		fetch_head->fp = NULL;
 	}
@@ -941,14 +943,17 @@  static void append_fetch_head(struct fetch_head *fetch_head,
 			return;
 	}
 
-	fprintf(fetch_head->fp, "%s\t%s\t%s",
-		oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
+	strbuf_addf(&fetch_head->buf, "%s\t%s\t%s",
+		    oid_to_hex_r(old_oid_hex, old_oid), merge_status_marker, note);
 	for (i = 0; i < url_len; ++i)
 		if ('\n' == url[i])
-			fputs("\\n", fetch_head->fp);
+			strbuf_addstr(&fetch_head->buf, "\\n");
 		else
-			fputc(url[i], fetch_head->fp);
-	fputc('\n', fetch_head->fp);
+			strbuf_addch(&fetch_head->buf, url[i]);
+	strbuf_addch(&fetch_head->buf, '\n');
+
+	strbuf_write(&fetch_head->buf, fetch_head->fp);
+	strbuf_reset(&fetch_head->buf);
 }
 
 static void commit_fetch_head(struct fetch_head *fetch_head)
@@ -962,6 +967,7 @@  static void close_fetch_head(struct fetch_head *fetch_head)
 		return;
 
 	fclose(fetch_head->fp);
+	strbuf_release(&fetch_head->buf);
 }
 
 static const char warn_show_forced_updates[] =