Comment 20 for bug 1678187

As for the patch, the following test shows that a file stored in /boot may require significantly more available space than the same file in /var/tmp, even if blocksize in (partition containing) /var/tmp is bigger. I don't know what is the best way to estimate how much available space is needed for storing a file in /boot.

$ echo $TMPDIR

$ echo $(( $(stat -f --format='%S' /boot ) ))
1024
$ echo $(( $(stat -f --format='%S' /var/tmp/ ) ))
4096
sudo dd if=/dev/zero of=/boot/file bs=K count=35553
35553+0 records in
35553+0 records out
36406272 bytes (36 MB) copied, 0,334945 s, 109 MB/s
$ sudo dd if=/dev/zero of=/var/tmp/file bs=K count=35553
35553+0 records in
35553+0 records out
36406272 bytes (36 MB) copied, 0,171743 s, 212 MB/s
$ echo $(( $(stat --format='%b*%B' /var/tmp/file ) ))
36409344
$ echo $(( $(stat --format='%b*%B' /boot/file ) ))
36549632