[PATCH] Cygwin: getdtablesize: always return OPEN_MAX_MAX

Corinna Vinschen corinna-cygwin@cygwin.com
Thu Jan 28 10:20:29 GMT 2021


On Jan 27 21:51, Ken Brown via Cygwin-patches wrote:
> According to the Linux man page for getdtablesize(3), the latter is
> supposed to return "the maximum number of files a process can have
> open, one more than the largest possible value for a file descriptor."
> The constant OPEN_MAX_MAX is the only limit enforced by Cygwin, so we
> now return that.
> 
> Previously getdtablesize returned the current size of cygheap->fdtab,
> Cygwin's internal file descriptor table.  But this is a dynamically
> growing table, and its current size does not reflect an actual limit
> on the number of open files.
> 
> With this change, gnulib now reports that getdtablesize and
> fcntl(F_DUPFD) work on Cygwin.  Packages like GNU tar that use the
> corresponding gnulib modules will no longer use gnulib replacements on
> Cygwin.
> ---
>  winsup/cygwin/syscalls.cc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
> index 5da05b18a..1f16d54b9 100644
> --- a/winsup/cygwin/syscalls.cc
> +++ b/winsup/cygwin/syscalls.cc
> @@ -2887,7 +2887,7 @@ setdtablesize (int size)
>  extern "C" int
>  getdtablesize ()
>  {
> -  return cygheap->fdtab.size;
> +  return OPEN_MAX_MAX;
>  }

getdtablesize is used internally, too.  After this change, the values
returned by sysconf and getrlimit should be revisited as well.


Thanks,
Corinna


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