Linux Device Drivers, Second Edition

The fs Directory

File handling is at the core of any Unix system, and the fs directory in Linux is the fattest of all directories. It includes all the filesystems supported by the current Linux version, each in its own subdirectory, as well as the most important system calls after fork and exit.

The execve system call lives in exec.c and relies on the various available binary formats to actually interpret the binary data found in the executable files. The most important binary format nowadays is ELF, implemented by binfmt_elf.c. binfmt_script.c supports the execution of interpreted files. After detecting the need for an interpreter (usually on the #! or “shebang” line), the file relies on the other binary formats to load the interpreter.

Miscellaneous binary formats (such as the Java executable format) can be defined by the user with a /proc interface defined in binfmt_misc.c. The misc binary format is able to identify an interpreted binary format based on the contents of the executable file, and fire the appropriate interpreter with appropriate arguments. The tool is configured via /proc/sys/fs/binfmt_misc.

The fundamental system calls for file access are defined in open.c and read_write.c. The former also defines close and several other file-access system calls (chown, for instance). select.c implements select and poll. pipe.c and fifo.c implement pipes and named pipes. readdir.c implements the getdents system call, which is how user-space programs read directories ...