There's a bug in this program. Can you spot it?
=====
#include <stdio.h>
int
main(int argc, char *argv[])
{
printf("Hello, world!\n");
return 0;
}
=====
The bug is that EDQUOT (Disk Quota exceeded:
/usr/include/asm-generic/errno.h) is not detected. If a shell
re-directs stdout into a file,
then the data might never be captured, and the problem would go
undetected until another program tries to read the file,
but does not find the expected data.
It is a very common programming error to omit the call to close() of an
output file, *AND/OR* not to check the return value of close().
["What could possibly go wrong?" Answer: EDQUOT or ENOSPC.]
Upon exit(), then the Linux kernel implicitly closes all open file
descriptors, but *IGNORES ALL ERRORS* in doing so. It's even documented
on the manpage: "Failing to check the return value when closing a file
may lead to silent loss of data. This can especially be observed with
NFS and with disk quota" [or when the output goes into a VM container.]
The app should call close() and check the return value. Before calling
close(), then a paranoid programmer will call fsync() (and check for
errors) in order to increase the reliability and integrity of data.
The C runtime library (package glibc) implementation of exit()
could help by calling close_range() of low-numbered output
[not input!] file descriptors, especially stdout, and checking
for errors.
The Linux kernel could help by not ignoring errors from close() when
called by exit(). If a signal cannot be delivered because too much
process state has been erased already, then the kernel should log
the first 5 errors per day.
--
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