[RFC] use buffered stdio (lightly tested)

[Eric Wong]

Our generation of HTML triggers many small write(2) syscalls
which is inefficient.

Time output on a horrible query against my git.git mirror
shows significant performance improvement:

QUERY_STRING=id=2b93bfac0f5bcabbf60f174f4e7bfa9e318e64d5&id2=d6da71a9d16b8cf27f9d8f90692d3625c849cbc8
PATH_INFO=/mirrors/git.git/diff
export QUERY_STRING PATH_INFO
time ./cgit >/dev/null

Before:
real    0m1.585s
user    0m0.904s
sys     0m0.658s

After:
real    0m0.750s
user    0m0.666s
sys     0m0.076s
---
 cache.c       |  7 +++++++
 cgit.c        |  2 +-
 filter.c      | 21 +++++++++++++--------
 html.c        |  2 +-
 ui-snapshot.c |  3 +++
 5 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/cache.c b/cache.c
index 2c70be7..580c0e8 100644
--- a/cache.c
+++ b/cache.c
@@ -265,6 +265,13 @@ static int process_slot(struct cache_slot *slot)
 {
 	int err;
 
+	/*
+	 * Make sure any buffered data is flushed before we redirect,
+	 * do sendfile(2) or write(2)
+	 */
+	if (fflush(stdout))
+		return errno;
+
 	err = open_slot(slot);
 	if (!err && slot->match) {
 		if (is_expired(slot)) {
diff --git a/cgit.c b/cgit.c
index 2f07e6d..55ba735 100644
--- a/cgit.c
+++ b/cgit.c
@@ -667,7 +667,7 @@ static inline void authenticate_post(void)
 		len = MAX_AUTHENTICATION_POST_BYTES;
 	if ((len = read(STDIN_FILENO, buffer, len)) < 0)
 		die_errno("Could not read POST from stdin");
-	if (write(STDOUT_FILENO, buffer, len) < 0)
+	if (fwrite(buffer, 1, len, stdout) < len)
 		die_errno("Could not write POST to stdout");
 	cgit_close_filter(ctx.cfg.auth_filter);
 	exit(0);
diff --git a/filter.c b/filter.c
index 70f5b74..2c387c1 100644
--- a/filter.c
+++ b/filter.c
@@ -48,6 +48,7 @@ static int open_exec_filter(struct cgit_filter *base, va_list ap)
 	for (i = 0; i < filter->base.argument_count; i++)
 		filter->argv[i + 1] = va_arg(ap, char *);
 
+	chk_zero(fflush(stdout), "unable to flush STDOUT");
 	filter->old_stdout = chk_positive(dup(STDOUT_FILENO),
 		"Unable to duplicate STDOUT");
 	chk_zero(pipe(pipe_fh), "Unable to create pipe to subprocess");
@@ -71,6 +72,7 @@ static int close_exec_filter(struct cgit_filter *base)
 	struct cgit_exec_filter *filter = (struct cgit_exec_filter *)base;
 	int i, exit_status = 0;
 
+	chk_zero(fflush(stdout), "unable to flush STDOUT");
 	chk_non_negative(dup2(filter->old_stdout, STDOUT_FILENO),
 		"Unable to restore STDOUT");
 	close(filter->old_stdout);
@@ -143,22 +145,22 @@ void cgit_init_filters(void)
 #endif
 
 #ifndef NO_LUA
-static ssize_t (*libc_write)(int fd, const void *buf, size_t count);
+static ssize_t (*libc_fwrite)(const void *buf, size_t size, size_t n, FILE *);
 static ssize_t (*filter_write)(struct cgit_filter *base, const void *buf, size_t count) = NULL;
 static struct cgit_filter *current_write_filter = NULL;
 
 void cgit_init_filters(void)
 {
-	libc_write = dlsym(RTLD_NEXT, "write");
-	if (!libc_write)
-		die("Could not locate libc's write function");
+	libc_fwrite = dlsym(RTLD_NEXT, "fwrite");
+	if (!libc_fwrite)
+		die("Could not locate libc's fwrite function");
 }
 
-ssize_t write(int fd, const void *buf, size_t count)
+size_t fwrite(const void *buf, size_t size, size_t n, FILE *f)
 {
-	if (fd != STDOUT_FILENO || !filter_write)
-		return libc_write(fd, buf, count);
-	return filter_write(current_write_filter, buf, count);
+	if (f != stdout || !filter_write)
+		return libc_fwrite(buf, size, n, f);
+	return filter_write(current_write_filter, buf, size * n);
 }
 
 static inline void hook_write(struct cgit_filter *filter, ssize_t (*new_write)(struct cgit_filter *base, const void *buf, size_t count))
@@ -305,6 +307,9 @@ static int open_lua_filter(struct cgit_filter *base, va_list ap)
 	struct lua_filter *filter = (struct lua_filter *)base;
 	int i;
 
+	if (fflush(stdout))
+		return 1;
+
 	if (init_lua_filter(filter))
 		return 1;
 
diff --git a/html.c b/html.c
index 138c649..ca9db91 100644
--- a/html.c
+++ b/html.c
@@ -80,7 +80,7 @@ char *fmtalloc(const char *format, ...)
 
 void html_raw(const char *data, size_t size)
 {
-	if (write(STDOUT_FILENO, data, size) != size)
+	if (fwrite(data, 1, size, stdout) != size)
 		die_errno("write error on html output");
 }
 
diff --git a/ui-snapshot.c b/ui-snapshot.c
index 9461d51..b9f03de 100644
--- a/ui-snapshot.c
+++ b/ui-snapshot.c
@@ -37,6 +37,9 @@ static int write_archive_type(const char *format, const char *hex, const char *p
 	/* argv_array guarantees a trailing NULL entry. */
 	memcpy(nargv, argv.argv, sizeof(char *) * (argv.argc + 1));
 
+	if (fflush(stdout))
+		return errno;
+
 	result = write_archive(argv.argc, nargv, NULL, the_repository, NULL, 0);
 	argv_array_clear(&argv);
 	free(nargv);
-- 
EW