On 2020-08-15 05:43, Rob Landley wrote:
On 8/13/20 10:02 AM, Rob Landley wrote:
On 8/11/20 2:25 PM, enh via Toybox wrote:
The key issues here turned out to be that getty is responsible for
creating the file if it doesn't exist, and that the -H flag doesn't
control whether utmp is updated, but whether or not to override the
hostname within the utmp entry.
While I'm here switch to the more modern utx APIs that all the non-pending
parts of toybox use, and remove the duplication.
Applied and pushed, but this reminds me I should really clean this up and
promote it.
The reason I haven't is I don't really have a test environment for it? (This
waits for a modem to dial in to a serial port, adjusts the baud rate, and calls
login. I got my first broadband connection in 2001 and haven't owned a modem
since.)
Do you have the FOGGIEST idea why:
xopen_stdio(TT.tty_name, O_RDWR|O_NDELAY|O_CLOEXEC);
fcntl(0, F_SETFL, fcntl(0, F_GETFL) & ~O_NONBLOCK); // Block read
O_NDELAY == O_NONBLOCK so it opens the tty nonblock and then immediately
switches off the nonblock. What (if anything) does that DO? Why is it here? Is
this something BSD 2.x needed in 1983 because of certain defective ASR-33
teletype variants when plugged into one of the HP minicomputers with the "zero
and add packed" instruction?
The man page is unenlightening, and the kernel source has 373 _files_ with
O_NONBLOCK in them...
In traditional SysV (with streams), O_NDELAY does not behave the same as
O_NONBLOCK.
In SysV, O_NDELAY means that a read from a file descriptor that does not
have any data (or a write which would extend the sendq length above the
kernel watermark) would immediately return 0 and not set an errno.
BSD also added O_NDELAY, which sets errno to EWOULDBLOCK and returns -1.
POSIX standardized the BSD implementation, adding the O_NONBLOCK flag
for it.
So, in SysV, this would give you a file descriptor that has "blocking"
reads but where the program itself does the blocking.
Ariadne
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