Linux swap file.

Documentation: Linux kernel source code, files:
 - mm/swapfile.c
 - include/linux/swap.h

Author: Victor Stinner
Creation date: 25 december 2006 (christmas ;-))

from hachoir_parser import Parser
from hachoir_core.field import (ParserError, GenericVector,
    UInt32, String,
    Bytes, NullBytes, RawBytes)
from hachoir_core.endian import LITTLE_ENDIAN
from hachoir_core.tools import humanFilesize
from hachoir_core.bits import str2hex

PAGE_SIZE = 4096

# Definition of MAX_SWAP_BADPAGES in Linux kernel:
#  (__swapoffset(magic.magic) - __swapoffset(info.badpages)) / sizeof(int)
MAX_SWAP_BADPAGES = ((PAGE_SIZE - 10) - 1536) // 4

class Page(RawBytes):
    static_size = PAGE_SIZE*8
    def __init__(self, parent, name):
        RawBytes.__init__(self, parent, name, PAGE_SIZE)

class UUID(Bytes):
    static_size = 16*8
    def __init__(self, parent, name):
        Bytes.__init__(self, parent, name, 16)
    def createDisplay(self):
        text = str2hex(self.value, format=r"%02x")
        return "%s-%s-%s-%s-%s" % (
            text[:8], text[8:12], text[12:16], text[16:20], text[20:])

class LinuxSwapFile(Parser):
        "id": "linux_swap",
        "file_ext": ("",),
        "category": "file_system",
        "min_size": PAGE_SIZE*8,
        "description": "Linux swap file",
        "magic": (
            ("SWAP-SPACE", (PAGE_SIZE-10)*8),
            ("SWAPSPACE2", (PAGE_SIZE-10)*8),
            ("S1SUSPEND\0", (PAGE_SIZE-10)*8),
    endian = LITTLE_ENDIAN

    def validate(self):
        magic = self.stream.readBytes((PAGE_SIZE-10)*8, 10)
        if magic not in ("SWAP-SPACE", "SWAPSPACE2", "S1SUSPEND\0"):
            return "Unknown magic string"
        if MAX_SWAP_BADPAGES < self["nb_badpage"].value:
            return "Invalid number of bad page (%u)" % self["nb_badpage"].value
        return True

    def getPageCount(self):
        Number of pages which can really be used for swapping:
        number of page minus bad pages minus one page (used for the header)
        # -1 because first page is used for the header
        return self["last_page"].value - self["nb_badpage"].value - 1

    def createDescription(self):
        if self["magic"].value == "S1SUSPEND\0":
            text = "Suspend swap file version 1"
        elif self["magic"].value == "SWAPSPACE2":
            text = "Linux swap file version 2"
            text = "Linux swap file version 1"
        nb_page = self.getPageCount()
        return "%s, page size: %s, %s pages" % (
            text, humanFilesize(PAGE_SIZE), nb_page)

    def createFields(self):
        # First kilobyte: boot sectors
        yield RawBytes(self, "boot", 1024, "Space for disklabel etc.")

        # Header
        yield UInt32(self, "version")
        yield UInt32(self, "last_page")
        yield UInt32(self, "nb_badpage")
        yield UUID(self, "sws_uuid")
        yield UUID(self, "sws_volume")
        yield NullBytes(self, "reserved", 117*4)

        # Read bad pages (if any)
        count = self["nb_badpage"].value
        if count:
            if MAX_SWAP_BADPAGES < count:
                raise ParserError("Invalid number of bad page (%u)" % count)
            yield GenericVector(self, "badpages", count, UInt32, "badpage")

        # Read magic
        padding = self.seekByte(PAGE_SIZE - 10, "padding", null=True)
        if padding:
            yield padding
        yield String(self, "magic", 10, charset="ASCII")

        # Read all pages
        yield GenericVector(self, "pages", self["last_page"].value, Page, "page")

        # Padding at the end
        padding = self.seekBit(self.size, "end_padding", null=True)
        if padding:
            yield padding
hachoir-parser documentation built on Sept. 20, 2017, 5:30 p.m.