[DragonFlyBSD - Bug #3282] unexpected errno value from fopen()

[jpipkin]

Issue #3282 has been updated by jpipkin.

File sys.kern.vfs_nlookup.c.diff added

Attached is a patch that fixes this. The interesting part is at:
--
@@ -921,7 +921,7 @@ nlookup(struct nlookupdata *nd) 
--

Note that a comment before the relevant section of code says:
--
Also handle invalid '.' or '..' components terminating a path        
for a create/rename/delete.  The standard requires this and pax      
pretty stupidly depends on it.
--

It's not clear exactly what pax depends on - just an error or EEXIST specifically - but it appears to behave normally with this change as far as I can tell. That said, I only tested a few simple cases with pax. Perhaps someone knows more about this.

Note also that attempting to open(2)/fopen(3) directories other than "." already produce the expected EISDIR. I believe they are covered by the following code from vn_open() in sys/kern/vfs_vnops.c:
--
 280         if ((fmode & O_CREAT) == 0) {                                           
 281                 if (fmode & (FWRITE | O_TRUNC)) {                               
 282                         if (vp->v_type == VDIR) {                               
 283                                 error = EISDIR;                                 
 284                                 goto bad;                                       
 285                         }
--


Perhaps someone with commit access can take a look at this.

----------------------------------------
Bug #3282: unexpected errno value from fopen()
http://bugs.dragonflybsd.org/issues/3282#change-14666

* Author: bhaible
* Status: New
* Priority: Normal
* Category: Kernel
* Target version: 6.4
* Start date: 2021-06-14
----------------------------------------
fopen(".", "w") fails with errno = EEXIST.
Per POSIX https://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
one would expect one of EISDIR, EINVAL, EACCES.

How to reproduce: Run this program.

<pre>
#include <errno.h>
#include <stdio.h>

int main ()
{
  FILE *fp = fopen (".", "w");
  if (fp == NULL)
    {
      perror ("fopen");
    }
}

</pre>

---Files--------------------------------
sys.kern.vfs_nlookup.c.diff (6.7 KB)


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