Can anyone file the following bug in parted for me (the bug tracker claims that it is spam and refuses to accept it)?
Bug title: Correctness of parted on MS-DOS partition constraints depends on
partition order
_log_meta_overlap_constraint in libparted/labels/dos.c does the following
questionable actions:
1. It walks the partitions in the order they are in the extended partition
linked list, assuming that they are ordered by their position on the disk.
2. It assumes it doesn't need to leave an empty sector at the beginning of the
fifth partition (the first in the linked list).
I couldn't find any documentation on the disk format to check whether the
metadata is before partitions or after them (from the code and comments of the
function I assume the former), but regardless of that, in both cases this
leads to the following problem:
When I start creating partitions starting from the end of the extended
partition and not the beginning, no space is left between the fifth (i.e. last
by position) and sixth (i.e. second but last) partition making the sector that
stores the information about the next partition also the first sector of the
fifth partition. Parted proceeds without giving an error. However, if you run
util-linux's fdisk and fix the partition order with it, parted refuses to load
the partition table any more.
I created the following partition table with parted (the snipped is *not*
actual fdisk output, I edited it by hand)
{{{
Device Boot Start End Blocks Id System
/dev/sdf1 2048 196607 97280 83 Linux
/dev/sdf4 196608 48859135 24331264 83 Linux
/dev/sdf3 48859136 60563455 5852160 83 Linux
/dev/sdf2 60565502 1953523711 946479105 f W95 Ext'd (LBA)
/dev/sdf6 60565504 80101375 9767936 83 Linux
/dev/sdf5 80101376 1953523711 936711168 83 Linux
}}}
Then used to fix the partition order and types with util-linux's fdisk, which
not only created a real overlap, it also made the partition table unopenable
by parted and applications using libparted. Got the following result (this
snipped *is* actual output).
{{{
Device Boot Start End Blocks Id System
/dev/sdf1 2048 196607 97280 fd Linux raid autodetect
/dev/sdf2 196608 48859135 24331264 fd Linux raid autodetect
/dev/sdf3 48859136 60563455 5852160 fd Linux raid autodetect
/dev/sdf4 60565502 1953523711 946479105 f W95 Ext'd (LBA)
/dev/sdf5 60565504 80101375 9767936 fd Linux raid autodetect
/dev/sdf6 80101376 1953523711 936711168 83 Linux
}}}
Before trying util-linux's fdisk, I tried to use GNU fdisk, and as expected,
it refused to fix the partition order because the fixed order violated the
constraint created by _log_meta_overlap_constraint, and after fixing it with
util-linux fdisk it also refused to open it completely.
In short, even if the partition table satisfying this constraint is
technically correct, such a partition table makes it impossible for you to
create another partition with the same partition sizes and position but
different partition order, for example to fix the partition order as fdisk
allows you to.
I suggest that:
1. Change min_start to be after the maximum of the endings of the partitions
whose start is before geom->start, walking all partitions in the partition
list. Change max_end to be the minimum of the starts of the partitions whose
end is after geom->end, again walking all partitions in the partition list.
2. Either place a free sector before every logical partition even the fifth, or
also ensure that that there is a free sector after every one that could
technically be followed by another partition. Possibly produce exceptions to
warn the user that there might be an overlap problem after possible future
reordering, and let him choose what action to take?
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