Added a function for setting the I/O semantics on a Coffee file descriptor. Changed the configuration parameters slightly and updated the platform definitions to reflect this change.

core/cfs/cfs-coffee.c

@@ -32,7 +32,13 @@
 
 /**
  * \file
- *	Coffee: A flash file system for memory-constrained sensor systems.
+ *	Coffee: A file system for a variety of storage types in
+ *              memory-constrained devices.
+ *
+ *	For further information, see "Enabling Large-Scale Storage in 
+ *      Sensor Networks with the Coffee File System" in the proceedings 
+ *      of ACM/IEEE IPSN 2009.
+ *
  * \author
  * 	Nicolas Tsiftes <nvt@sics.se>
  */
@@ -53,14 +59,35 @@
 #include "cfs-coffee-arch.h"
 #include "cfs/cfs-coffee.h"
 
-#ifndef COFFEE_CONF_APPEND_ONLY
+/* Micro logs enable modifications on storage types that do not support
-#define COFFEE_APPEND_ONLY	0
+   in-place updates. This applies primarily to flash memories. */
-#else
+#ifndef COFFEE_MICRO_LOGS
-#define COFFEE_APPEND_ONLY	COFFEE_CONF_APPEND_ONLY
+#define COFFEE_MICRO_LOGS	1
-#if COFFEE_MICRO_LOGS
-#error "Cannot have COFFEE_APPEND_ONLY when COFFEE_MICRO_LOGS is set."
 #endif
-#define COFFEE_MICRO_LOGS	0
+
+/* If the files are expected to be appended to only, this parameter 
+   can be set to save some code space. */
+#ifndef COFFEE_APPEND_ONLY
+#define COFFEE_APPEND_ONLY	0
+#endif
+
+#if COFFEE_MICRO_LOGS && COFFEE_APPEND_ONLY
+#error "Cannot have COFFEE_APPEND_ONLY set when COFFEE_MICRO_LOGS is set."
+#endif
+
+/* I/O semantics can be set on file descriptors in order to optimize 
+   file access on certain storage types. */
+#ifndef COFFEE_IO_SEMANTICS
+#define COFFEE_IO_SEMANTICS	0
+#endif
+
+/*
+ * Prevent sectors from being erased directly after file removal.
+ * This will level the wear across sectors better, but may lead
+ * to longer garbage collection procedures.
+ */
+#ifndef COFFEE_EXTENDED_WEAR_LEVELLING
+#define COFFEE_EXTENDED_WEAR_LEVELLING	1
 #endif
 
 #if COFFEE_START & (COFFEE_SECTOR_SIZE - 1)
@@ -149,6 +176,9 @@ struct file_desc {
   cfs_offset_t offset;
   struct file *file;
   uint8_t flags;
+#ifdef COFFEE_IO_SEMANTICS
+  uint8_t io_flags;
+#endif
 };
 
 /* The file header structure mimics the representation of file headers 
@@ -579,7 +609,7 @@ remove_by_page(coffee_page_t page, int remove_log, int close_fds,
     }
   }
 
-#if !COFFEE_CONF_EXTENDED_WEAR_LEVELLING
+#if !COFFEE_EXTENDED_WEAR_LEVELLING
   if(gc_allowed) {
     collect_garbage(GC_RELUCTANT);
   }
@@ -1137,6 +1167,9 @@ cfs_write(int fd, const void *buf, unsigned size)
   file = fdp->file;
 
   /* Attempt to extend the file if we try to write past the end. */
+#ifdef COFFEE_IO_SEMANTICS
+  if(!(fdp->io_flags & CFS_COFFEE_IO_FIRM_SIZE)) {
+#endif
   while(size + fdp->offset + sizeof(struct file_header) >
      (file->max_pages * COFFEE_PAGE_SIZE)) {
     if(merge_log(file->page, 1) < 0) {
@@ -1145,9 +1178,17 @@ cfs_write(int fd, const void *buf, unsigned size)
     file = fdp->file;
     PRINTF("Extended the file at page %u\n", (unsigned)file->page);
   }
+#ifdef COFFEE_IO_SEMANTICS
+  }
+#endif
 
 #if COFFEE_MICRO_LOGS
+#if COFFEE_IO_SEMANTICS
+  if(!(fdp->io_flags & CFS_COFFEE_IO_TOGGLE_ONLY) &&
+     (FILE_MODIFIED(file) || fdp->offset < file->end)) {
+#else
   if(FILE_MODIFIED(file) || fdp->offset < file->end) {
+#endif
     for(bytes_left = size; bytes_left > 0;) {
       lp.offset = fdp->offset;
       lp.buf = buf;
@@ -1280,6 +1321,20 @@ cfs_coffee_configure_log(const char *filename, unsigned log_size,
   return 0;
 }
 /*---------------------------------------------------------------------------*/
+#ifdef COFFEE_IO_SEMANTICS
+int
+cfs_coffee_set_io_semantics(int fd, unsigned flags)
+{
+  if(!FD_VALID(fd)) {
+    return -1;
+  }
+
+  coffee_fd_set[fd].io_flags |= flags;
+
+  return 0;
+}
+#endif
+/*---------------------------------------------------------------------------*/
 int
 cfs_coffee_format(void)
 {

core/cfs/cfs-coffee.h

@@ -40,6 +40,29 @@
 
 #include "cfs.h"
 
+/**
+ * Instruct Coffee that the access pattern to this file is adapted to 
+ * flash I/O semantics by design, and Coffee should therefore not 
+ * invoke its own micro logs when file modifications occur.
+ *
+ * This semantical I/O setting is useful when implementing flash storage
+ * algorithms on top of Coffee.
+ *
+ * \sa cfs_coffee_set_io_semantics()
+ */
+#define CFS_COFFEE_IO_TOGGLE_ONLY 0x1
+
+/**
+ * Instruct Coffee not to attempt to extend the file when there is
+ * an attempt to write past the reserved file size.
+ *
+ * A case when this is necessary is when the file has a firm size limit,
+ * and a safeguard is needed to protect against writes beyond this limit.
+ *
+ * \sa cfs_coffee_set_io_semantics()
+ */
+#define CFS_COFFEE_IO_FIRM_SIZE   0x2
+
 /**
  * \file
  *	Header for the Coffee file system.
@@ -65,9 +88,9 @@ int cfs_coffee_reserve(const char *name, cfs_offset_t size);
 
 /**
  * \brief Configure the on-demand log file.
- * \param file
+ * \param file The filename.
- * \param log_size
+ * \param log_size The total log size.
- * \param log_entry_size
+ * \param log_entry_size The log entry size.
  * \return 0 on success, -1 on failure.
  *
  * When file data is first modified, Coffee creates a micro log for the
@@ -78,6 +101,21 @@ int cfs_coffee_reserve(const char *name, cfs_offset_t size);
 int cfs_coffee_configure_log(const char *file, unsigned log_size,
                              unsigned log_entry_size);
 
+/**
+ * \brief Set the I/O semantics for accessing a file.
+ *
+ * \param fd The file descriptor through which the file is accessed.
+ * \param flags A bit vector of flags.
+ *
+ * Coffee is used on a wide range of storage types, and the default 
+ * I/O file semantics may not be optimal for the access pattern 
+ * of a certain file. Hence, this functions allows programmers to 
+ * switch the /O semantics on a file that is accessed through a 
+ * particular file descriptor.
+ *
+ */
+int cfs_coffee_set_io_semantics(int fd, unsigned flags);
+
 /**
  * \brief Format the storage area assigned to Coffee.
  * \return 0 on success, -1 on failure.

platform/native/cfs-coffee-arch.h

@@ -55,6 +55,7 @@
 #define COFFEE_LOG_SIZE			8192
 #define COFFEE_LOG_TABLE_LIMIT		256
 #define COFFEE_MICRO_LOGS		0
+#define COFFEE_IO_SEMANTICS		1
 
 #define COFFEE_WRITE(buf, size, offset)				\
 		xmem_pwrite((char *)(buf), (size), COFFEE_START + (offset))

platform/sky/cfs-coffee-arch.h

@@ -55,6 +55,8 @@
 #define COFFEE_DYN_SIZE			4*1024
 #define COFFEE_LOG_SIZE			1024
 
+#define COFFEE_IO_SEMANTICS		1
+#define COFFEE_APPEND_ONLY		0
 #define COFFEE_MICRO_LOGS		1
 
 /* Flash operations. */