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Date: Fri, 03 Feb 2012 13:11:00 -0000
From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: [RFA/gdbserver] Provide dummy readlink on systems where routine is not available.
In-reply-to: <20120203123030.GJ31383@adacore.com>
To: Joel Brobecker <brobecker@adacore.com>
Cc: gdb-patches@sourceware.org, palves@redhat.com
Reply-to: Eli Zaretskii <eliz@gnu.org>
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References: <1328269562-19101-1-git-send-email-brobecker@adacore.com> <1328270124-27388-1-git-send-email-brobecker@adacore.com> <20120203123030.GJ31383@adacore.com>
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> Date: Fri, 3 Feb 2012 16:30:30 +0400
> From: Joel Brobecker <brobecker@adacore.com>
> Cc: palves@redhat.com
> 
> Another revised version, with 2 small changes:
>   - The pre-processor condition used to determine whether we need to
>     declare readlink in gdb_readlink.h or not was wrong. Somehow,
>     HAVE_ macros and HAVE_DECL_ macros are handled differently.
>   - I forgot to update hostio.c's dependency on gdb_readlink.h
>     in the Makefile.
> 
> Both issues now fixed, and new patch attached.

If memory serves, Pedro was against this when I suggested it.

> +   This function return -1 (error) and sets errno to ENOSYS to indicate
> +   that this function is not implemented.  The caller should be prepared
> +   to recover from that.  */

But the function in fact returns EINVAL:

> +ssize_t
> +readlink(const char *path, char *buf, size_t bufsiz)
> +{
> +  errno = EINVAL;
> +  return -1;
> +}

I cannot resist re-iterating my original suggestion: test the file for
existence, return ENOENT if it doesn't exist, and otherwise return
EINVAL, meaning that the file is not a link.

Or just use the readlink module from gnulib, which does exactly that.