[k3b] [Bug 444920] New: k3b calculates size incorrectly when deciding when size of media was exceeded

[Ken Arromdee]

https://bugs.kde.org/show_bug.cgi?id=444920

            Bug ID: 444920
           Summary: k3b calculates size incorrectly when deciding when
                    size of media was exceeded
           Product: k3b
           Version: unspecified
          Platform: Mageia RPMs
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: Burning/Hardware
          Assignee: k3b at kde.org
          Reporter: arromdee at gmx.com
                CC: michalm at jabster.pl, trueg at kde.org
  Target Milestone: ---

SUMMARY


STEPS TO REPRODUCE
1. Try to burn a BD-R containing files that seem to almost fill a BD-R


OBSERVED RESULT
The bottom bar will report "Available: ___ of 23.3 GB".  The burn will fail
with "mkisofs crashed" and the log shows "no space left on device".  The bar
will then show that the capacity is exceeded, even though it didn't think the
capacity was exceeded when you started to burn.  In this case it claims that I
have Available: 165.6 MB, but after the burn fails, it says capacity is
exceeded by 90.4 MB.

EXPECTED RESULT
The amount available when I start should be accurate, so that if I exceeded
capacity by 90.4 MB, it says that instead of falsely claiming there is space
available.

SOFTWARE/OS VERSIONS
Linux: Linux version 5.10.52-desktop-1.mga8 (iurt at ec2x1.mageia.org) (gcc
(Mageia 10.3.0-1.mga8) 10.3.0, GNU ld (GNU Binutils) 2.36.1) #1 SMP Tue Jul 20
17:00:24 UTC 2021
KDE Plasma Version: None (running just fvwm3)
k3b version is 20.12.0 which is not listed above.

ADDITIONAL INFORMATION
I have had this problem over many versions of k3b.  It is not new.  I don't
think it is limited to BDs .  If you do have enough space for the burn, the
amount available will still go down when you burn it, just not by enough to
cause an error.

The difference between the available space at the start and at the end is
exactly 256M.  On computers, the number 256 looks suspicious.  Also, the
difference seems too small to be a 1000/1024 mixup.

The log file shows that the mkisofs result has a size of 24852099072. 
Cursoring to the bottom bar shows that the  files total to 24851695616 which is
not the same number but close.  A BD-R is supposed to have 25025315816 bytes
which is indeed about 165M (using powers of 2) over.  cdrwtool shows track size
12219392 which multiplied by 2048 gives the expected 25025315816.

The extra space may be used up by overhead, but if so, I have no idea where the
overhead comes from, and k3b really should not tell you there is available
space when there is not because of overhead.  I have Multisession: No and don't
know about other possible sources of overhead.

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