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dev: read /dev/zero and /dev/urandom from them, not from the keyboard

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consoleinit() put consoleread/consolewrite in devsw[1], over memread and
memwrite. Major 1 holds the whole mem major (null, zero, full, random,
urandom) and memread already sends the console's minors to the console,
so the override only broke the others: a read of /dev/zero waited for a
typed line. dd and head on either device hung, and `head -c 10 /dev/zero`
only finished because it swallowed the next command.

The console now installs just its open and close hooks. /dev/keyboard
writes are discarded, as consolewrite used to do.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
This commit is contained in:
Nexoniarz 2026-10-23 09:33:08 +02:00
commit d90a72e6d3
3 changed files with 15 additions and 2 deletions
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8
docs/architecture/devices.md
View file

@ -355,6 +355,14 @@ from the cycle counter on each byte so two readers do not continue one
sequence. What changed is the property that made it dangerous rather than
merely poor.
**For a long time it could not be read at all**, and neither could `/dev/zero`.
Both are minors of major 1, and `devsw[1]` is `memread`/`memwrite`, which hand
the console's minors to the console and the rest to their own functions. But
`consoleinit()` installed `consoleread` over the whole major, so a read of
`/dev/zero` waited for a line from the keyboard. `head -c 10 /dev/zero`
"worked" by taking the next command typed. The console now installs only its
`open` and `close` hooks.
## What it does not do
- **It is a flat list, not a device tree.** There is no parent/child nesting,

8
kernel/core/console.c
View file

@ -820,8 +820,12 @@ consoleinit(void)
initlock(&cons.lock, "console");
initlock(&input_lock, "input");
devsw[CONSOLE].write = consolewrite;
devsw[CONSOLE].read = consoleread;
// Not read and write. Major 1 is the whole mem major -- null, zero, full,
// random, urandom as well as the console and the ttys -- and devsw[1] is
// memread/memwrite, which send the console's minors here and the rest
// where they belong. Installing consoleread over it made /dev/zero and
// /dev/urandom wait for a line from the keyboard, which is why neither
// had ever seemed to work.
devsw[CONSOLE].open = consoleopen;
devsw[CONSOLE].close = consoleclose;
cons.locking = 1;

1
kernel/dev/cdev.c
View file

@ -170,6 +170,7 @@ memwrite(struct inode *ip, uint64 off, char *dst, int n)
case 10: case 11: case 12: case 13: case 14: case 15: case 16:
return consolewrite(ip, off, dst, n);
case 7: return fullwrite(ip, off, dst, n); // /dev/full: always ENOSPC
case 3: // /dev/keyboard: discarded
case 2:
case 5:
case 8: