MEMFS(2) MEMFS(2)
NAME
memfs - heap based filesystem
SYNOPSIS
include "sys.m";
include "memfs.m";
memfs := load MemFS MemFS->PATH;
init: fn(): string;
newfs: fn(maxsz: int): ref Sys->FD;
DESCRIPTION
The MemFS module implements a Styx file server where all
files and filesystem data structures are stored in the local
heap, not on disk.
init()
The init function should be called once to initialise
the internal state of MemFS. Failure to initialise is
reported by the returned string. A return value of nil
indicates success.
newfs(maxsz)
The newfs function takes a single argument, maxsz
defining the maximum number of bytes of the new
filesystem. The return value is a file descriptor,
serving Styx, suitable for passing to mount (see sys-
bind(2)).
Multiple filesystems of different sizes can be supported by
a single instance of the module. Each filesystem is con-
strained by maxsz, any filesystem operations that cause the
limit to be exceeded are failed with the error message:
`filesystem full'
File data is allocated in 512 byte blocks. The actual
filesystem data limit is always a multiple of this block
size:
actualmaxsz := (maxsz / 512) * 512;
SOURCE
/appl/lib/memfs.b
CAVEATS
Only file data blocks are considered in the determination of
heap usage, the overhead of internal data structures cannot
be accounted for. MemFS could store its own data structures
in data blocks, but this would impede performance.
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MEMFS(2) MEMFS(2)
Newly created and empty files are pre-allocated a data block
in an attempt to prevent directory entries from using heap
without regard to the requested maxsz.
SEE ALSO
styxlib(2), memfs(4)
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