On Wed, 11 Dec 2024 at 11:28, John Reiser <jreiser@xxxxxxxxxxxx> wrote:
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.
I have seen this listed as NOT A BUG even with realtime programmers because the application can be run in all kinds of ways which could induce failures that are 'environment' versus 'application'. I expect it depends on the exact environment but what is the correct code? Something like the following?
===
#include <stdio.h>
#include <stdlib.h>
// This would be better with subroutines but this is supposed to be
// hello world.
int main(int argc, char *argv[]){
int err=0;
err=printf("Hello, world!\n");
if (err < 0){ // we got an error somewhere
err=fclose(stdout);
if (err != 0){ // we got a bigger error
return err;
}
err=fclose(stderr);
if (err != 0){ // we got a bigger error
return err;
}
return 1;
} else {
err=fclose(stdout);
if (err != 0){ // we got a bigger error
return err;
}
err=fclose(stderr);
if (err != 0){ // we got a bigger error
return err;
}
return 0;
}
}
===
Stephen Smoogen, Red Hat Automotive
Let us be kind to one another, for most of us are fighting a hard battle. -- Ian MacClaren-- _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx 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/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
