[PATCH 2/3 v2] cache: use sendfile() instead of a pair of read() + write()

[Sebastian Andrzej Siewior]

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 HAVE_LINUX_SENDFILE in case the OS (kernel & libc)
supports the Linux/glibc interface. It is disabled by default on non-linux
environments. 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>
---
On Sat, Jun 23, 2012 at 10:27:25AM +0000, Ben Boeckel wrote:
> On Thu, Jun 21, 2012 at 07:09:47 GMT, cgit at ml.breakpoint.cc wrote:
> > From: Sebastian Andrzej Siewior <sebastian at breakpoint.cc>
> > +ifneq ($(uname_S),Linux)
> > +	NO_SENDFILE = YesPlease
> > +endif
> 
> Double negatives suck. Can the option be made HAVE_SENDFILE?
Yes it does. What about this.

 Makefile |    9 +++++++++
 cache.c  |   26 +++++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index eac24ad..20cae98 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,8 @@ 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 HAVE_LINUX_SENDFILE to use sendfile() as offered by glibc on Linux.
+#
 
 #-include config.mak
 
@@ -49,6 +51,10 @@ ifeq ($(uname_O),Cygwin)
 	NEEDS_LIBICONV = YesPlease
 endif
 
+ifeq ($(uname_S),Linux)
+	HAVE_LINUX_SENDFILE = YesPlease
+endif
+
 #
 # Let the user override the above settings.
 #
@@ -157,6 +163,9 @@ ifdef NO_OPENSSL
 else
 	EXTLIBS += -lcrypto
 endif
+ifdef HAVE_LINUX_SENDFILE
+	CFLAGS	+= -DHAVE_LINUX_SENDFILE
+endif
 
 cgit: $(OBJECTS) libgit
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o cgit $(OBJECTS) $(EXTLIBS)
diff --git a/cache.c b/cache.c
index d7a8d5a..963ec3a 100644
--- a/cache.c
+++ b/cache.c
@@ -13,6 +13,9 @@
  *
  */
 
+#ifdef HAVE_LINUX_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 +83,23 @@ 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 HAVE_LINUX_SENDFILE
+	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);
+#else
 	ssize_t i, j;
 
 	i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
@@ -97,6 +116,7 @@ static int print_slot(struct cache_slot *slot)
 		return errno;
 	else
 		return 0;
+#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