Any Linux swap partition unfortunately must be created explicitely
for the platform where it will be used. Currently this implementation
autodetects the values (like endianity) needed for
during its compilation, existing partitions are detected platform
independently. Please don't rely on the ordering of value of each of the
parameter - these are compilation-type dependent just to have the default
value always as the first choice.
Default Version 1 if possible is autodected by the run time code stored in autoheader() function called from swap_fs_mkfs(). The value is dependent on pagesize, warning is generated depending on currently running kernel version.
Compilation-time detected by G_BYTE_ORDER dependant
inits.c, set by glib library.
Compilation-time detected by SWAP_PAGESIZE_* macros from
params.h.m4 source, currently uses system offered PAGE_SIZE
When we encounter some already created partition, we have to guess and/or detect its parameters as it can be principially created on foreign platform. All these detections are done in swap_read_super.
We try to recognize swap partition header from the smaller (
to larger (
8192) pagesize. During reuse of the partition, the smaller
one gets certainly overwritten by larger pagesize, in the opposite direction
we could falsely detected old (and not used) larger header.
Version is easily detectable by its "
SWAP-SPACE" (ver. 1)
SWAPSPACE2" (ver. 2) magic string. Please note that
these strings don't follow the endianity in any way.
This detection depends on the (well) detected header version:
This is the only a bit nonreliable swap manager part. We currently
believe that swap page (in
pagesize counting) #24 is not marked
as bad. Swap page #0 is always non-used, there must be bit 0. When
we find also bit 0 on the position for swap page #24, we just give
warning to the user and guess the endianity as the endianity of
the platform where is
Surprise currently running.
Easy task, we currently support (only exists) "
1 given as "
unsigned int", endianity is determinable
by swapping the bytes.
We build the block #0 (starting in swap_fs_mkfs) in endianity of our
current platform, badblocks (in
Version 2 header) are not sorted.
When badblocks count is exceeded during the creation (for
Version 2 header),
we will refuse (with error return) to continue the operation. The
proper endianity is swapped (together with possible badblocks sorting)
just before writing of the block in swap_fs_fsdone.
As we are general filesystem of
Surprise project, a foolish user may
want to for example convert existing filesystem to
Linux swap type.
We are refusing to create any files or directiories in swap_fs_check.