cache: use sendfile() instead of a pair of read() + write()

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@breakpoint.cc>

3 files changed, 34 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 2dc92df..05b97d7 100644
--- a/Makefile
+++ b/Makefile
@@ -29,6 +29,7 @@ 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()
 
 #-include config.mak
 
diff --git a/cache.c b/cache.c
index fcd461f..9e7eeb0 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"
 #include "html.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();
 
+        /* update stat info */
+        if (fstat(slot->lock_fd, &slot->cache_st))
+                return errno;
+
         /* Restore stdout */
         if (dup2(tmp, STDOUT_FILENO) == -1)
                 return errno;
diff --git a/cgit.mk b/cgit.mk
index 056c3f9..3b8b79a 100644
--- a/cgit.mk
+++ b/cgit.mk
@@ -68,6 +68,14 @@ ifeq ($(findstring BSD,$(uname_S)),)
         CGIT_LIBS += -ldl
 endif
 
+# glibc 2.1+ offers sendfile which the most common C library on Linux
+ifeq ($(uname_S),Linux)
+        HAVE_LINUX_SENDFILE = YesPlease
+endif
+
+ifdef HAVE_LINUX_SENDFILE
+        CGIT_CFLAGS += -DHAVE_LINUX_SENDFILE
+endif
 
 CGIT_OBJ_NAMES += cgit.o
 CGIT_OBJ_NAMES += cache.o