I think you may be confusing /dev/zero and /dev/null. /dev/null (as its name suggests) returns NULL values, not zeroes.

On Fri, Nov 15, 2019 at 7:26 AM Juha Nikkanen nikkej@gmail.com wrote:

Ladies and gentlemen,

I have curious problem after booting into 5.3.11. I can't read a stream of zeroes from /dev/null anymore: $ dd if=/dev/null of=zero.dat bs=2048 count=1 0+0 records in 0+0 records out 0 bytes copied, 0.00036764 s, 0.0 kB/s

and: $ file /dev/null /dev/null: character special (1/3) $ ls -l /dev/null crw-rw-rw-. 1 root root 1, 3 Nov 14 20:28 /dev/null No matter if I try this as a root or as a ordinary user. Results are exactly same. I did not test this with kernels 5.3.7 and 5.3.8, I jumped to 5.3.11 from 5.3.6 and I think 5.3.6 did provide a stream of zero data. No strace gives anything special, just ordinary read() after dup2() and read returns zero length for 2048 requested. Now is this a problem of kernel or is it within dd and how it opens a /dev/null or how it flags read() function?

Sincerely, Juha _______________________________________________ kernel mailing list -- kernel@lists.fedoraproject.org To unsubscribe send an email to kernel-leave@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/kernel@lists.fedoraproject.org