Michael Devore wrote:
At 04:01 PM 7/21/2005 -0500, I wrote:
When you invoke FDISK without arguments, it goes into the
Interactive_User_Interface() routine. That, in turn, asks about FAT32
support, via Ask_User_About_FAT32_Support() function. OK so far.
After that call -- without any further prompting -- FDISK calls the
Create_MBR_If_Not_Present() routine.
NO. Please, no. You should never write to the hard disk for
low-level stuff like partitions and master boot record data without
warning and giving the user a chance to abort or decide not to do it.
Second related issue...the Create_MBR_If_Not_Present() routine receives
an error code if Read_Physical_Sectors() routine fails, but the error
code is not checked. Consequently, should the routine to read physical
sectors fail for any reason and return an error, the following occurs:
The buffer which was not loaded by the read is still tested for valid
values and if they fail to match what was expected (as they likely will)
a new MBR is written.
That is probably the wrong approach to handling an error on the
low-level disk read. Particularly at startup.
I have a work in progress towards fixing these issues of fdisk,
to try my current build - http://www.fdos.org/kernel/test/fdisk.exe
Currently I have it so it delays actual writing of MBR to disk until
just before program exit (so if you reboot or in advanced mode abort
your changes, the mbr=CHS(0,0,1) should be unmodified). It also now
aborts on read error with a message. Note: fdisk may still write to
other sectors than mbr during use, eg boot sector of partition. This
build also has a pause and message that shows the disks the MBR is being
written to. I'll continue working on this a little while longer, but
this build is here for feedback.
Jeremy
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