From 15edf7b671340d674777d5244d16629359c27ec5 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Wed, 2 Jan 2008 18:15:47 +1100
Subject: [PATCH] added pread_cache.c

---
 pread_cache.c | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 pread_cache.c

diff --git a/pread_cache.c b/pread_cache.c
new file mode 100644
index 0000000..af8306a
--- /dev/null
+++ b/pread_cache.c
@@ -0,0 +1,127 @@
+/*
+  pread_cache.c: a cache to map pread() calls to fread() to prevent small
+  reads on MacOSX network filesystems that don't do block cacheing
+
+  tridge@samba.org January 2008
+
+  released under GNU GPLv3 or later
+  
+  to compile on MacOSX:
+    gcc pread.c -Wall -g -o pread.dylib -dynamiclib 
+
+  usage:
+
+    DYLD_INSERT_LIBRARIES=/Users/tridge/pread.dylib DYLD_FORCE_FLAT_NAMESPACE=1 command
+
+*/
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <dlfcn.h>
+#include <errno.h>
+
+/* chosen to match the smbfs on MacOSX read size */
+#define MAX_READ 61000
+
+/* to keep the data structures simple, we only cache the low MAX_FILES file descriptors */
+#define MAX_FILES 1024
+static FILE *file_handles[MAX_FILES];
+static unsigned char file_state[MAX_FILES];
+
+#define STATE_NONE    0
+#define STATE_CACHED  1
+#define STATE_DISABLE 2
+
+/* catch close to free up any existing caches */
+int close(int fd)
+{
+	static int (*close_orig)(int fd);
+	if (close_orig == NULL) {
+		close_orig = dlsym(RTLD_NEXT, "close");
+		if (close_orig == NULL) {
+			abort();
+		}
+	}
+	if (fd < 0 || fd >= MAX_FILES) {
+		return close_orig(fd);
+	}
+
+	if (file_state[fd] == STATE_CACHED) {
+		FILE *f;
+		file_state[fd] = STATE_NONE;
+		f = file_handles[fd];
+		file_handles[fd] = NULL;
+		/* the fclose() does an implied close() */
+		return fclose(f);
+	}
+
+	file_state[fd] = STATE_NONE;
+	return close_orig(fd);
+}
+
+/*
+  catch pread() and if possible map to fread()
+ */
+ssize_t pread(int fd, void *buf, size_t nbytes, off_t offset)
+{
+	static ssize_t (*pread_orig)(int d, void *buf, size_t nbytes, off_t offset);
+	static int pagesize;
+
+	if (pread_orig == NULL) {
+		pread_orig = dlsym(RTLD_NEXT, "pread");
+		if (pread_orig == NULL) {
+			abort();
+		}
+		pagesize = getpagesize();
+	}
+
+	/* large reads and reads on out of range file descriptors are not cached */
+	if (nbytes >= MAX_READ || fd < 0 || fd >= MAX_FILES) {
+		return pread_orig(fd, buf, nbytes, offset);
+	}
+
+	if (file_state[fd] == STATE_DISABLE) {
+		return pread_orig(fd, buf, nbytes, offset);		
+	}
+
+	/* see if we already have a cache */
+	if (file_state[fd] == STATE_NONE) {
+		void *ptr;
+
+		/* see if the file was opened read-write. This relies on the mmap error codes */
+		ptr = mmap(NULL, pagesize, PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED, fd, 0);
+		if (ptr != (void *)-1) {
+			munmap(ptr, pagesize);
+			file_state[fd] = STATE_DISABLE;
+			return pread_orig(fd, buf, nbytes, offset);		
+		}
+		if (errno != EACCES) {
+			file_state[fd] = STATE_DISABLE;
+			return pread_orig(fd, buf, nbytes, offset);
+		}
+
+		file_handles[fd] = fdopen(fd, "r");
+		if (file_handles[fd] == NULL) {
+			file_state[fd] = STATE_DISABLE;
+			return pread_orig(fd, buf, nbytes, offset);
+		}
+
+		/* ensure we have a big enough buffer */
+		setvbuf(file_handles[fd], NULL, _IOFBF, MAX_READ);
+
+		file_state[fd] = STATE_CACHED;
+	}
+
+	/* seek to the right place if need be */
+	if (ftello(file_handles[fd]) != offset &&
+	    fseeko(file_handles[fd], offset, SEEK_SET) != 0) {
+		return pread_orig(fd, buf, nbytes, offset);
+	}
+
+	return fread(buf, 1, nbytes, file_handles[fd]);
+}
+
-- 
2.34.1