[PATCH 2/3] cache: use sendfile() instead of a pair of read() + write()

[cgit at ml.breakpoint.cc]

From: Sebastian Andrzej Siewior <sebastian at breakpoint.cc>

sendfile() does the same job and avoids to copy the content into userland
and back. One has to define NO_SENDFILE in case the OS (kernel / libc)
does not supported. It is disabled by default on non-linux environemnts.
According to the glibc, sendfile64() was added in Linux 2.4 (so it has
been there for a while) but after browsing over the mapage of FreeBSD's I
noticed that the prototype is little different.

Signed-off-by: Sebastian Andrzej Siewior <sebastian at breakpoint.cc>
---
 Makefile |   10 ++++++++++
 cache.c  |   26 +++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index eac24ad..5cc84f4 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,9 @@ DOC_PDF  = $(patsubst %.txt,%.pdf,$(MAN_TXT))
 # j, z, t. (representing long long int, char, intmax_t, size_t, ptrdiff_t).
 # some C compilers supported these specifiers prior to C99 as an extension.
 #
+# Define NO_SENDFILE to avoid using the sendfile() offered by libc. Use this
+# if your OS does not provide support for sendfile()
+#
 
 #-include config.mak
 
@@ -49,6 +52,10 @@ ifeq ($(uname_O),Cygwin)
 	NEEDS_LIBICONV = YesPlease
 endif
 
+ifneq ($(uname_S),Linux)
+	NO_SENDFILE = YesPlease
+endif
+
 #
 # Let the user override the above settings.
 #
@@ -157,6 +164,9 @@ ifdef NO_OPENSSL
 else
 	EXTLIBS += -lcrypto
 endif
+ifdef NO_SENDFILE
+	CFLAGS	+= -DNO_SENDFILE
+endif
 
 cgit: $(OBJECTS) libgit
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o cgit $(OBJECTS) $(EXTLIBS)
diff --git a/cache.c b/cache.c
index d7a8d5a..19bbc11 100644
--- a/cache.c
+++ b/cache.c
@@ -13,6 +13,9 @@
  *
  */
 
+#ifndef NO_SENDFILE
+#include <sys/sendfile.h>
+#endif
 #include "cgit.h"
 #include "cache.h"
 
@@ -30,7 +33,6 @@ struct cache_slot {
 	const char *lock_name;
 	int match;
 	struct stat cache_st;
-	struct stat lock_st;
 	int bufsize;
 	char buf[CACHE_BUFSIZE];
 };
@@ -81,6 +83,7 @@ static int close_slot(struct cache_slot *slot)
 /* Print the content of the active cache slot (but skip the key). */
 static int print_slot(struct cache_slot *slot)
 {
+#ifdef NO_SENDFILE
 	ssize_t i, j;
 
 	i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
@@ -97,6 +100,23 @@ static int print_slot(struct cache_slot *slot)
 		return errno;
 	else
 		return 0;
+#else
+	off_t start_off;
+	int ret;
+
+	start_off = slot->keylen + 1;
+
+	do {
+		ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
+				slot->cache_st.st_size - start_off);
+		if (ret < 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				continue;
+			return errno;
+		}
+		return 0;
+	} while (1);
+#endif
 }
 
 /* Check if the slot has expired */
@@ -188,6 +208,10 @@ static int fill_slot(struct cache_slot *slot)
 	/* Generate cache content */
 	slot->fn(slot->cbdata);
 
+	/* update stat info */
+	if (fstat(slot->lock_fd, &slot->cache_st))
+		return errno;
+
 	/* Restore stdout */
 	if (dup2(tmp, STDOUT_FILENO) == -1)
 		return errno;
-- 
1.7.2.5