Date: Sat, 21 Jul 2001 14:47:29 +0100 From: Ian Dowse <iedowse@maths.tcd.ie> To: freebsd-hackers@freebsd.org Subject: fdisk(8) adjusting to head/cylinder bounderies Message-ID: <200107211447.aa29342@salmon.maths.tcd.ie>
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For about a year, fdisk(8) has had code that automatically adjusts
partitions to begin on a head boundary and end on a cylinder
boundary. This is fine in most situations, but the way it is
implemented makes it awkward to override, and more importantly it
is way too easy to mess up an existing partition that is not properly
aligned on a head/cylinder boundary.
Currently, fdisk never asks the user for confirmation of changes
to the partition start and size. It just prints out a message
such as
WARNING: adjusting start offset of partition
to 12345 to fall on a head boundary
and then it immediately goes on to print out the full slice details,
so that warning is easily missed. It is possible to avoid the
automatic adjustment by answering "y" to the
Explicitly specify beg/end address?
question that refers to setting the c/h/s parameters, but if you
do that, then you can't make use of the automatic c/h/s calculation.
This problem bites me almost every time I use fdisk, since we have
a lot of disks that have been split into multiple partitions to
get around the 7 partitions/slice limit. I have always just changed
the slice to end exactly where the last partition ends, so having
fdisk rounding that down by a few sectors is not desirable. These
disks are generally SCSI, contain only FreeBSD partitions, and the
BIOSes we work with have never had problems with partitions that
are not head/cylinder aligned.
Below is a patch that makes fdisk request user confirmation before
making any changes to the start and end of partitions. It also
untangles the automatic c/h/s calculation from the start/size
adjustment, and doesn't set the partition type to 0 if the
adjustment fails.
I haven't put a great deal of thought into the specifics of the
patch, so any comments or suggestions are welcome. I just want to
avoid the behaviour where carefully calculated partition parameters
supplied by the user get changed automatically with only an easily-
missed warning printed.
Ian
Index: fdisk.c
===================================================================
RCS file: /dump/FreeBSD-CVS/src/sbin/i386/fdisk/fdisk.c,v
retrieving revision 1.50
diff -u -r1.50 fdisk.c
--- fdisk.c 2001/07/13 16:48:56 1.50
+++ fdisk.c 2001/07/21 12:02:01
@@ -548,6 +548,7 @@
Decimal("sysid (165=FreeBSD)", partp->dp_typ, tmp);
Decimal("start", partp->dp_start, tmp);
Decimal("size", partp->dp_size, tmp);
+ sanitize_partition(partp);
if (ok("Explicitly specify beg/end address ?"))
{
@@ -572,8 +573,6 @@
partp->dp_esect = DOSSECT(tsec,tcyl);
partp->dp_ehd = thd;
} else {
- if (!sanitize_partition(partp))
- partp->dp_typ = 0;
dos(partp->dp_start, partp->dp_size,
&partp->dp_scyl, &partp->dp_ssect, &partp->dp_shd);
dos(partp->dp_start + partp->dp_size - 1, partp->dp_size,
@@ -1398,6 +1397,17 @@
max_end = partp->dp_start + partp->dp_size;
+ if (partp->dp_start % dos_sectors != 0 ||
+ (partp->dp_start + partp->dp_size) % dos_sectors != 0) {
+ if (partp->dp_start % dos_sectors != 0)
+ warnx("WARNING: partition does not begin on a head boundary");
+ if ((partp->dp_start + partp->dp_size) % dos_sectors != 0)
+ warnx("WARNING: partition does not end on a cylinder boundary");
+ warnx("WARNING: this may confuse the BIOS or other operating systems");
+ if (!ok("Correct this automatically?"))
+ return(1);
+ }
+
/*
* Adjust start upwards, if necessary, to fall on an head boundary.
*/
@@ -1412,9 +1422,7 @@
"ERROR: unable to adjust start of partition to fall on a head boundary");
return (0);
}
- warnx(
- "WARNING: adjusting start offset of partition\n\
- to %u to fall on a head boundary",
+ warnx("WARNING: adjusting start offset of partition to %u",
(u_int)(prev_head_boundary + dos_sectors));
partp->dp_start = prev_head_boundary + dos_sectors;
}
@@ -1434,10 +1442,7 @@
return (0);
}
if (adj_size != partp->dp_size) {
- warnx(
- "WARNING: adjusting size of partition to %u to end on a\n\
- cylinder boundary",
- (u_int)adj_size);
+ warnx("WARNING: adjusting size of partition to %u", (u_int)adj_size);
partp->dp_size = adj_size;
}
if (partp->dp_size == 0) {
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