packer/vendor/github.com/mitchellh/go-fs

FAT Filesystem Library for Go

This library implements the ability to create, read, and write FAT filesystems using pure Go.

WARNING: While the implementation works (to some degree, see the limitations section below), I highly recommend you don't use this library, since it has many limitations and is generally a terrible implementation of FAT. For educational purposes, however, this library may be interesting.

In this library's current state, it is very good for reading FAT filesystems, and minimally useful for creating FAT filesystems. See the features and limitations below.

Features & Limitations

Features:

• Format a brand new FAT filesystem on a file backed device
• Create files and directories
• Traverse filesystem

Limitations:

This library has several limitations. They're easily able to be overcome, but because I didn't need them for my use case, I didn't bother:

• Files/directories cannot be deleted or renamed.
• Files never shrink in size.
• Deleted file/directory entries are never reclaimed, so fragmentation grows towards infinity. Eventually, your "disk" will become full even if you just create and delete a single file.
• There are some serious corruption possibilities in error cases. Cleanup is not good.
• Incomplete FAT32 implementation (although FAT12 and FAT16 are complete).

Usage

Here is some example usage where an existing disk image is read and a file is created in the root directory:

// Assume this file was created already with a FAT filesystem
f, err := os.OpenFile("FLOPPY.dmg", os.O_RDWR|os.O_CREATE, 0666)
if err != nil {
	panic(err)
}
defer f.Close()

// BlockDevice backed by a file
device, err := fs.NewFileDisk(f)
if err != nil {
	panic(err)
}

filesys, err := fat.New(device)
if err != nil {
	panic(err)
}

rootDir, err := filesys.RootDir()
if err != nil {
	panic(err)
}

subEntry, err := rootDir.AddFile("HELLO_WORLD")
if err != nil {
	panic(err)
}

file, err := subEntry.File()
if err != nil {
	panic(err)
}

_, err = io.WriteString(file, "I am the contents of this file.")
if err != nil {
	panic(err)
}

Thanks

Thanks to the following resources which helped in the creation of this library:

• fat32-lib
• File Allocation Table on Wikipedia
• Microsoft FAT filesystem specification