Re: Defect in XBD limits.h

["Steve Schwarm, W3EVE" <yyyyy@xxxxxxxxxxxxx>]

I believe the description is correct.  A process can not open more than 
OPEN_MAX files.  That does not mean than a file descriptor can not be > 
OPEN_MAX.  I suspect it could be in some implementations.

Steve Schwarm

Geoff Clare wrote:

> @ page 248 line 8724 section limits.h objection [gwc OPEN_MAX]
>
> Problem:
>
> Defect code :  1. Error
>
> The description of OPEN_MAX on the limits.h page is:
>
>    {OPEN_MAX}
>       Maximum number of files that one process can have open at any
>       one time.
>
> This is fine if OPEN_MAX is a constant defined in limits.h, but if
> the limit varies then I believe the description does not match
> current behaviour in the case where a file descriptor >= OPEN_MAX is
> already open.
>
> I do not think current systems keep an independent count of open file
> descriptors.  They search for the first available file descriptor and
> if they reach OPEN_MAX without finding one then they give an EMFILE
> error.  The standard does not currently allow this behaviour - it
> requires an EMFILE error when OPEN_MAX file descriptors are open,
> even if some file descriptors numbered less than OPEN_MAX are still
> available.
>
> The problem can be solved either by changing the description of
> OPEN_MAX, the description of EMFILE in the "Error Numbers" section
> of XSH6, and the descriptions of EMFILE for individual functions in
> XSH6; or by forbidding the situation where a fd >= OPEN_MAX is open.
> Note that I proposed the latter in March 2002 (along with the change
> that allowed sysconf(_SC_OPEN_MAX) to return different values before
> and after a call to setrlimit() that changes RLIMIT_NOFILE), and it
> was rejected then.  However, this new aspect of the "fd >= OPEN_MAX"
> problem has come to light since then and so was not taken into account.
>
> Action:
>
> Either
>
> 1. Change "Maximum number of files that one process can have open at
> any one time" to "A value one greater than the maximum value that the
> system may assign to a newly-created file descriptor".
>
> On XSH6 page 24 lines 964-965 change:
>
>    "[EMFILE]
>        Too many open files. An attempt was made to open more than the
>        maximum number of file descriptors allowed in this process."
>
> to:
>
>    "[EMFILE]
>        File descriptor too large.  An attempt was made to open a file
>        descriptor with a value greater than or equal to {OPEN_MAX},
>        [XSI] or greater than or equal to the soft RLIMIT_NOFILE limit
>        for the process (if smaller than {OPEN_MAX}).[/XSI]"
>
> and make suitable changes to the EMFILE descriptions on individual
> function pages.
>
> Or
>
> 2. Insert before XSH6 page 1469 line 45443, "The value returned by
> sysconf(_SC_OPEN_MAX) shall be either -1 or a value greater than
> the highest currently open file descriptor."