Linux: Support File Operations

Question

Has someone maybe a good source where all available file operations like fopen, fread, mkdir, etc are described? When I am googleing for Linux file operations most pages explain me how the filesystem hierarchy looks like.

Answer 1

Yep -- use the man pages. man fopen, man fread, man mkdir, etc., will describe the usage of those functions. Many man pages also have a "See Also" section that will direct you to the man pages of related functions, sort of like a primitive Wikipedia. :)

Answer 2

I 'm not sure if this helps, but this is directly out of the kernel source:

struct file_operations {
    struct module *owner;
    loff_t (*llseek) (struct file *, loff_t, int);
    ssize_t (*read) (struct file *, char *, size_t, loff_t *);
    ssize_t (*write) (struct file *, const char *, size_t, loff_t *);
    int (*readdir) (struct file *, void *, filldir_t);
    unsigned int (*poll) (struct file *, struct poll_table_struct *);
    int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
    int (*mmap) (struct file *, struct vm_area_struct *);
    int (*open) (struct inode *, struct file *);
    int (*flush) (struct file *);
    int (*release) (struct inode *, struct file *);
    int (*fsync) (struct file *, struct dentry *, int datasync);
    int (*fasync) (int, struct file *, int);
    int (*lock) (struct file *, int, struct file_lock *);
    ssize_t (*readv) (struct file *, const struct iovec *, unsigned long, loff_t *);
    ssize_t (*writev) (struct file *, const struct iovec *, unsigned long, loff_t *);
    ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
    unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
};

Filesystems generally register all their implementations to these callbacks.

Answer 3

The functions you're asking about actually fall under several categories - file stream I/O (fopen, fread, etc.), lower-level file descriptor I/O (open, read, etc.), and filesystem/directory manipulation (chown, mkdir, etc.).

For an overview of file stream I/O functions, see man stdio.

For searching Google, try "posix file api" instead of "linux file operations."

You can also check the GNU C Libary Manual:

• Input/Output on Streams
• Low-Level Input/Output
• File System Interface

Answer 4

use man 2 open and man 2 mkdir. at the bottom of this man pages are the name of related command.

Alternatively, if you search a browseable version of this man pages, you can try here

Answer 5

There a several file operations APIs on different levels of the stack, e.g. POSIX API, Standard C API, Linux VFS API (as Jeremy mentioned), and the FUSE API. All the APIs do more or less the same thing, but the details are very different.

• fopen and fread are members of the standard C file (stream) operations. Links: GNU Documentation
• mkdir is member of the POSIX file API. Links: OpenGroup Definition, GNU Documentation

These two APIs are the most important for the normal user.

A good book about the topic is "Advanced Programming in the UNIX Environment" by Stevens and Rago