Contiki Coffee File System

Introduction

This tutorial is a introduction to cfs_open function of Coffee file system on Contiki OS 2.7.

You Will Learn

Through this tutorial you will learn about how the Coffee file system works.

Source Code

~/contiki-2.7/core/cfs/cfs-coffee.h ~/contiki-2.7/core/cfs/cfs-coffee.c

Coffee File System Open File

Data Structure Used In The System

struct file_desc {
  cfs_offset_t offset;
  struct file *file;
  uint8_t flags;
#if COFFEE_IO_SEMANTICS
  uint8_t io_flags;
#endif
};

struct file_desc coffee_fd_set[COFFEE_FD_SET_SIZE];

cfs_open

cf_open is used to open a file. If it successfully open the file then it returns the file descriptor(fd), otherwise it returns -1.
cfs_open source code:

int
cfs_open(const char *name, int flags)
{
  int fd;
  struct file_desc *fdp;

  fd = get_available_fd();
  if(fd < 0) {
    PRINTF("Coffee: Failed to allocate a new file descriptor!\n");
    return -1;
  }

  fdp = &coffee_fd_set[fd];
  fdp->flags = 0;

  fdp->file = find_file(name);
  if(fdp->file == NULL) {
    if((flags & (CFS_READ | CFS_WRITE)) == CFS_READ) {
      return -1;
    }
    fdp->file = reserve(name, page_count(COFFEE_DYN_SIZE), 1, 0);
    if(fdp->file == NULL) {
      return -1;
    }
    fdp->file->end = 0;
  } else if(fdp->file->end == UNKNOWN_OFFSET) {
    fdp->file->end = file_end(fdp->file->page);
  }

  fdp->flags |= flags;
  fdp->offset = flags & CFS_APPEND ? fdp->file->end : 0;
  fdp->file->references++;

  return fd;
}