Open, Part 2

Objectives

1. Understand more of the options when opening a file.

Notes

• The man page/book lists many different options we can use when opening a file.
• We need to look at these to get the flavor of operation.
• I will look at a few
• O_APPEND always write to the end of the file
  • This is important later. (Just like O_RDWR)
• O_CLOEXEC close on exec
  • We will discuss this one later as well.
• O_DIRECT try not to cache/buffer this file
  • Used with O_SYNC to require synchronous I/O
  • Otherwise advisory to the OS
• O_EXCL
  • When creating a file, fail if the pathname already exists.
  • This is to force creation of a new file.
• O_TRUNC
  • If the file exists, truncate to length 0.
• O_TMPFILE
  • Construct a tempory file
  • This will be removed when the last file descriptor is closed
  • In this case, pathname specifies a directory where the file will be created
  • Must be opened with O_RDWR or O_WRONLY
  • There is a discussion on how the file can be preserved if needed.
• There are more, but not now.
• int creat(const char *pathname, mode_t mode);
  • A convience routine for calling open with O_CREAT|O_WRONLY|O_TRUNC