ramfs

package module
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 Go to latest Published: Jan 11, 2015 License: ISC Imports: 8 Imported by: 0

README

RAMFS

Ramfs starts a 9P2000 file server keeping all files in memory. The filesystem is entirely maintained in memory, no external storage is used. File data is allocated in 2 MiB blocks.

The root of the filesystem is owned by the user who invoked ramfs and is created with Read, Write and Execute permissions for the owner and Read and Execute permissions for everyone else (0755). Ramfs create the necessary directories and files in /adm/ctl, /adm/group and /.

9P2000

A 9P2000 server is an agent that provides one or more hierarchical file systems -- file trees -- that may be accessed by processes. A server responds to requests by clients to navigate the hierarchy, and to create, remove, read, and write files.

References

Usage

To add a new user with name and id gnot and create his home directory:

echo uname gnot gnot | racon write /adm/group

To create a new group sys (with no home directory) and add gnot to it:

echo uname sys :sys | racon write /adm/group
echo uname sys +gnot | racon write /adm/group

Listen manages the network addresses at which ramfs is listening.

echo listen tcp localhost:5641 | racon write /adm/ctl

Documentation

Overview

Package ramfs implements a 9P2000 file server keeping all files in memory.

A 9P2000 server is an agent that provides one or more hierarchical file systems -- file trees -- that may be accessed by processes. A server responds to requests by clients to navigate the hierarchy, and to create, remove, read, and write files.

References: 

[intro]   http://plan9.bell-labs.com/magic/man2html/5/0intro
[attach]  http://plan9.bell-labs.com/magic/man2html/5/attach
[clunk]   http://plan9.bell-labs.com/magic/man2html/5/clunk
[error]   http://plan9.bell-labs.com/magic/man2html/5/error
[flush]   http://plan9.bell-labs.com/magic/man2html/5/flush
[open]    http://plan9.bell-labs.com/magic/man2html/5/open
[read]    http://plan9.bell-labs.com/magic/man2html/5/read
[remove]  http://plan9.bell-labs.com/magic/man2html/5/remove
[stat]    http://plan9.bell-labs.com/magic/man2html/5/stat
[version] http://plan9.bell-labs.com/magic/man2html/5/version
[walk]    http://plan9.bell-labs.com/magic/man2html/5/walk

Index

Constants

View Source 
const (
	MSIZE = 128*1024 + plan9.IOHDRSZ // maximum message size
	// IOUNIT represents the maximum size that is guaranteed to be
	// transferred atomically.
	IOUNIT    = 128 * 1024
	BLOCKSIZE = 2 * 1024 * 1024 // maximum block size

	OREAD   = plan9.OREAD   // open for read
	OWRITE  = plan9.OWRITE  // open for write
	ORDWR   = plan9.ORDWR   // open for read/write
	OEXEC   = plan9.OEXEC   // read but check execute permission
	OTRUNC  = plan9.OTRUNC  // truncate file first
	ORCLOSE = plan9.ORCLOSE // remove on close
	OEXCL   = plan9.OEXCL   // exclusive use
	OAPPEND = plan9.OAPPEND // append only

	QTDIR    = plan9.QTDIR    // type bit for directories
	QTAPPEND = plan9.QTAPPEND // type bit for append only files
	QTEXCL   = plan9.QTEXCL   // type bit for exclusive use files
	QTAUTH   = plan9.QTAUTH   // type bit for authentication file
	QTTMP    = plan9.QTTMP    // type bit for non-backed-up file
	QTFILE   = plan9.QTFILE   // type bits for plain file

	DMDIR    = plan9.DMDIR    // mode bit for directories
	DMAPPEND = plan9.DMAPPEND // mode bit for append only files
	DMEXCL   = plan9.DMEXCL   // mode bit for exclusive use files
	DMAUTH   = plan9.DMAUTH   // mode bit for authentication file
	DMTMP    = plan9.DMTMP    // mode bit for non-backed-up file
	DMREAD   = plan9.DMREAD   // mode bit for read permission
	DMWRITE  = plan9.DMWRITE  // mode bit for write permission
	DMEXEC   = plan9.DMEXEC   // mode bit for execute permission
)

RamFS constants and limits.

Variables

This section is empty.

Functions

This section is empty.

Types

type FS 

type FS struct {
	Log LogFunc
	// contains filtered or unexported fields
}

FS represents a a 9P2000 file server.

func New 

func New(hostowner string) *FS

New starts a 9P2000 file server keeping all files in memory. The filesystem is entirely maintained in memory, no external storage is used. File data is allocated in 128 * 1024 byte blocks.

The root of the filesystem is owned by the user who invoked ramfs and is created with Read, Write and Execute permissions for the owner and Read and Execute permissions for everyone else (0755). FS create the necessary directories and files in /adm/ctl, /adm/group and /<hostowner>.

func (*FS) Attach 

func (fs *FS) Attach(uname, aname string) (*Fid, error)

Attach identifies the user and may select the file tree to access. As a result of the attach transaction, the client will have a connection to the root directory of the desired file tree, represented by Fid.

func (*FS) Create 

func (fs *FS) Create(name string, mode uint8, perm Perm) (*Fid, error)

Create asks the file server to create a new file with the name supplied, in the directory represented by fid, and requires write permission in the directory. The owner of the file is the implied user id of the request, the group of the file is the same as dir, and the permissions are the value of 

perm = (perm &^ 0666) | (dir.Mode & 0666)

if a regular file is being created and 

perm = (perm &^ 0777) | (dir.Mode & 0777)

if a directory is being created.

Finally, the newly created file is opened according to mode, and fid will represent the newly opened file. Directories are created by setting the DMDIR bit (0x80000000) in the perm.

The names . and .. are special; it is illegal to create files with these names.

func (*FS) Halt 

func (fs *FS) Halt() error

Halt closes the filesystem, rendering it unusable for I/O.

func (*FS) Listen 

func (fs *FS) Listen(network, addr string) error

Listen listens on the given network address and then serves incoming requests.

func (*FS) Open 

func (fs *FS) Open(name string, mode uint8) (*Fid, error)

Open asks the file server to check permissions and prepare a fid for I/O with subsequent read and write messages. The mode field determines the type of I/O: OREAD, OWRITE, ORDWR, and OEXEC mean read access, write access, read and write access, and execute access, to be checked against the permissions for the file.

In addition, if mode has the OTRUNC bit set, the file is to be truncated, which requires write permission (if the file is append–only, and permission is granted, the open succeeds but the file will not be truncated); if the mode has the ORCLOSE bit set, the file is to be removed when the fid is clunked, which requires permission to remove the file from its directory.

It is illegal to write a directory, truncate it, or attempt to remove it on close. If the file is marked for exclusive use, only one client can have the file open at any time.

func (*FS) Remove 

func (fs *FS) Remove(name string) error

Remove asks the file server both to remove the file represented by fid and to clunk the fid, even if the remove fails.

type Fid 

type Fid struct {
	New *Fid
	// contains filtered or unexported fields
}

The Fid type identifies a file on the file server. A new Fid is created when the user attaches to the file server, or when Walk-ing to a file. The Fid values are created automatically by the ramfs implementation.

func (*Fid) Close 

func (f *Fid) Close() error

Close informs the file server that the current file represented by fid is no longer needed by the client.

func (*Fid) Create 

func (f *Fid) Create(name string, mode uint8, perm Perm) error

Create asks the file server to create a new file with the name supplied, in the directory represented by fid, and requires write permission in the directory. The owner of the file is the implied user id of the request, the group of the file is the same as dir, and the permissions are the value of 

perm = (perm &^ 0666) | (dir.Mode & 0666)

if a regular file is being created and 

perm = (perm &^ 0777) | (dir.Mode & 0777)

if a directory is being created.

Finally, the newly created file is opened according to mode, and fid will represent the newly opened file. Directories are created by setting the DMDIR bit (0x80000000) in the perm.

The names . and .. are special; it is illegal to create files with these names.

func (*Fid) Open 

func (f *Fid) Open(mode uint8) error

Open asks the file server to check permissions and prepare a fid for I/O with subsequent read and write messages. The mode field determines the type of I/O: OREAD, OWRITE, ORDWR, and OEXEC mean read access, write access, read and write access, and execute access, to be checked against the permissions for the file.

In addition, if mode has the OTRUNC bit set, the file is to be truncated, which requires write permission (if the file is append–only, and permission is granted, the open succeeds but the file will not be truncated); if the mode has the ORCLOSE bit set, the file is to be removed when the fid is clunked, which requires permission to remove the file from its directory.

It is illegal to write a directory, truncate it, or attempt to remove it on close. If the file is marked for exclusive use, only one client can have the file open at any time.

func (*Fid) ReadAt 

func (f *Fid) ReadAt(p []byte, offset int64) (int, error)

ReadAt asks for len(p) bytes of data from the file identified by fid, which must be opened for reading, starting offset bytes after the beginning of the file.

For directories, ReadAt returns an integral number of directory entries exactly as in stat, one for each member of the directory.

func (*Fid) Remove 

func (f *Fid) Remove() error

Remove asks the file server both to remove the file represented by fid and to clunk the fid, even if the remove fails.

func (*Fid) Stat 

func (f *Fid) Stat() ([]byte, error)

Stat inquires about the file identified by fid. The reply will contain a machine-independent directory entry

func (*Fid) Walk 

func (f *Fid) Walk(name []string, fn WalkFunc) error

Walk walks the file tree.

func (*Fid) WriteAt 

func (f *Fid) WriteAt(p []byte, offset int64) (int, error)

WriteAt asks that len(p) bytes of data be recorded in the file identified by fid, which must be opened for writing, starting offset bytes after the beginning of the file. If the file is append–only, the data will be placed at the end of the file regardless of offset. Directories may not be written.

WriteAt records the number of bytes actually written. It is usually an error if this is not the same as requested.

func (*Fid) Wstat 

func (f *Fid) Wstat(data []byte) error

Wstat can change some of the file status information. The name can be changed by anyone with write permission in the parent directory; it is an error to change the name to that of an existing file.

The mode can be changed by the owner of the file or the group leader of the file's current group. The directory bit cannot be changed by a wstat; the other defined permission and mode bits can. The gid can be changed: by the owner if also a member of the new group; or by the group leader of the file's current group if also leader of the new group.

Either all the changes in Wstat request happen, or none of them does: if the request succeeds, all changes were made; if it fails, none were.

type LogFunc 

type LogFunc func(format string, v ...interface{})

LogFunc can be used to enable a trace of general debugging messages.

type Perm 

type Perm uint32

Perm represents file/directory permissions.

func (Perm) String 

func (p Perm) String() string

type WalkFunc 

type WalkFunc func(fid *Fid, path []string) error

WalkFunc is the type of the function called for each file or directory visited by Walk.

Source Files

View all Source files

Directories

Path Synopsis
cmd
racon
Usage: racon [options] cmd [option] args...
 Usage: racon [options] cmd [option] args...
ramfs
Usage: ramfs [options] Ramfs starts a 9P2000 file server keeping all files in memory.
 Usage: ramfs [options] Ramfs starts a 9P2000 file server keeping all files in memory.

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