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Re: Crash on -current on i386 (NOT amd64)

On Dec 5,  1:57pm, (John Nemeth) wrote:
-- Subject: Re: Crash on -current on i386 (NOT amd64)

|      I don't think there was a backtrace.  I saw your comment on
| chat that you had fixed the lseek(SEEK_END) issue, and was curious
| what it was, so I looked for the commit, and spotted the bug.  I
| then saw Paul's message about his crash about mounting a CD and
| noted your new DIAGNOSTIC message about DIOCGMEDIASIZE failing in
| his output, which hinted that it was your patch.  At first, I was
| going to suggest that he revert it, but then decided that I could
| fix it (I don't know anything about file system code, so normally
| don't go anywhere near it).
|      The issues goes like this.  The original code in pseudo code
| format (with irrelevant details omitted goes like this):
| 1) ioctl(DIOCGPART)
| 2) if successful
| 3)   use struct partinfo to determine disk size
| 4)   call uvm_vnp_setsize(disk size)
| Your new code did:
| 2) if failure
| 3)   diagnostic(DIOCGMEDIASIZE failed)
| 4)   ioctl(DIOCGPART)
| 5)   use struct partinfo to determine disk size
| 6) if either ioctl was successful
| 7)   call uvm_vnp_setsize(disk size)
| Note that at step 5, you were dereferencing two pointers in struct
| partinfo regardless of whether or not the ioctl(DIOCGPART) was
| successful, which is what initializes the struct partinfo.  I just
| did the obvious and inserted step 4.5, "if successful", to avoid
| dereferencing NULL pointers.

Yes, I know.

|      The implication of all this is that the CD driver in question
| doesn't support either DIOCGMEDIASIZE or DIOCGPART.  Thus for the
| CD driver, there is no functional difference between the original
| code and your new code (with my fix).

Hmm, there should be a backtrace though and we could fix the driver...
Actually I want to get rid of most of the disklabel code (leaving
behind the DEFLABEL code for a new 64 bit struct.


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