open_buffer(
    int		read_stdin,	    // read file from stdin
    exarg_T	*eap,		    // for forced 'ff' and 'fenc' or NULL
    int		flags)		    // extra flags for readfile()
{
    int		retval = OK;
    bufref_T	old_curbuf;
#ifdef FEAT_SYN_HL
    long	old_tw = curbuf->b_p_tw;
#endif
    int		read_fifo = FALSE;

    // The 'readonly' flag is only set when BF_NEVERLOADED is being reset.
    // When re-entering the same buffer, it should not change, because the
    // user may have reset the flag by hand.
    if (readonlymode && curbuf->b_ffname != NULL
					&& (curbuf->b_flags & BF_NEVERLOADED))
	curbuf->b_p_ro = TRUE;

    if (ml_open(curbuf) == FAIL)
    {
	// There MUST be a memfile, otherwise we can't do anything
	// If we can't create one for the current buffer, take another buffer
	close_buffer(NULL, curbuf, 0, FALSE, FALSE);
	FOR_ALL_BUFFERS(curbuf)
	    if (curbuf->b_ml.ml_mfp != NULL)
		break;
	// If there is no memfile at all, exit.
	// This is OK, since there are no changes to lose.
	if (curbuf == NULL)
	{
	    emsg(_(e_cannot_allocate_any_buffer_exiting));

	    // Don't try to do any saving, with "curbuf" NULL almost nothing
	    // will work.
	    v_dying = 2;
	    getout(2);
	}

	emsg(_(e_cannot_allocate_buffer_using_other_one));
	enter_buffer(curbuf);
#ifdef FEAT_SYN_HL
	if (old_tw != curbuf->b_p_tw)
	    check_colorcolumn(curwin);
#endif
	return FAIL;
    }

    // The autocommands in readfile() may change the buffer, but only AFTER
    // reading the file.
    set_bufref(&old_curbuf, curbuf);
    modified_was_set = FALSE;

    // mark cursor position as being invalid
    curwin->w_valid = 0;

    if (curbuf->b_ffname != NULL
#ifdef FEAT_NETBEANS_INTG
	    && netbeansReadFile
#endif
       )
    {
	int old_msg_silent = msg_silent;
#ifdef UNIX
	int save_bin = curbuf->b_p_bin;
	int perm;
#endif
#ifdef FEAT_NETBEANS_INTG
	int oldFire = netbeansFireChanges;

	netbeansFireChanges = 0;
#endif
#ifdef UNIX
	perm = mch_getperm(curbuf->b_ffname);
	if (perm >= 0 && (S_ISFIFO(perm)
		      || S_ISSOCK(perm)
# ifdef OPEN_CHR_FILES
		      || (S_ISCHR(perm) && is_dev_fd_file(curbuf->b_ffname))
# endif
		    ))
		read_fifo = TRUE;
	if (read_fifo)
	    curbuf->b_p_bin = TRUE;
#endif
	if (shortmess(SHM_FILEINFO))
	    msg_silent = 1;
	retval = readfile(curbuf->b_ffname, curbuf->b_fname,
		  (linenr_T)0, (linenr_T)0, (linenr_T)MAXLNUM, eap,
		  flags | READ_NEW | (read_fifo ? READ_FIFO : 0));
#ifdef UNIX
	if (read_fifo)
	{
	    curbuf->b_p_bin = save_bin;
	    if (retval == OK)
		retval = read_buffer(FALSE, eap, flags);
	}
#endif
	msg_silent = old_msg_silent;
#ifdef FEAT_NETBEANS_INTG
	netbeansFireChanges = oldFire;
#endif
	// Help buffer is filtered.
	if (bt_help(curbuf))
	    fix_help_buffer();
    }
    else if (read_stdin)
    {
	int	save_bin = curbuf->b_p_bin;

	// First read the text in binary mode into the buffer.
	// Then read from that same buffer and append at the end.  This makes
	// it possible to retry when 'fileformat' or 'fileencoding' was
	// guessed wrong.
	curbuf->b_p_bin = TRUE;
	retval = readfile(NULL, NULL, (linenr_T)0,
		  (linenr_T)0, (linenr_T)MAXLNUM, NULL,
		  flags | (READ_NEW + READ_STDIN));
	curbuf->b_p_bin = save_bin;
	if (retval == OK)
	    retval = read_buffer(TRUE, eap, flags);
    }

    // if first time loading this buffer, init b_chartab[]
    if (curbuf->b_flags & BF_NEVERLOADED)
    {
	(void)buf_init_chartab(curbuf, FALSE);
	parse_cino(curbuf);
    }

    // Set/reset the Changed flag first, autocmds may change the buffer.
    // Apply the automatic commands, before processing the modelines.
    // So the modelines have priority over autocommands.
    //
    // When reading stdin, the buffer contents always needs writing, so set
    // the changed flag.  Unless in readonly mode: "ls | gview -".
    // When interrupted and 'cpoptions' contains 'i' set changed flag.
    if ((got_int && vim_strchr(p_cpo, CPO_INTMOD) != NULL)
		|| modified_was_set	// ":set modified" used in autocmd
#ifdef FEAT_EVAL
		|| (aborting() && vim_strchr(p_cpo, CPO_INTMOD) != NULL)
#endif
       )
	changed();
    else if (retval == OK && !read_stdin && !read_fifo)
	unchanged(curbuf, FALSE, TRUE);
    save_file_ff(curbuf);		// keep this fileformat

    // Set last_changedtick to avoid triggering a TextChanged autocommand right
    // after it was added.
    curbuf->b_last_changedtick = CHANGEDTICK(curbuf);
    curbuf->b_last_changedtick_i = CHANGEDTICK(curbuf);
    curbuf->b_last_changedtick_pum = CHANGEDTICK(curbuf);

    // require "!" to overwrite the file, because it wasn't read completely
#ifdef FEAT_EVAL
    if (aborting())
#else
    if (got_int)
#endif
	curbuf->b_flags |= BF_READERR;

#ifdef FEAT_FOLDING
    // Need to update automatic folding.  Do this before the autocommands,
    // they may use the fold info.
    foldUpdateAll(curwin);
#endif

    // need to set w_topline, unless some autocommand already did that.
    if (!(curwin->w_valid & VALID_TOPLINE))
    {
	curwin->w_topline = 1;
#ifdef FEAT_DIFF
	curwin->w_topfill = 0;
#endif
    }
#ifdef FEAT_EVAL
    apply_autocmds_retval(EVENT_BUFENTER, NULL, NULL, FALSE, curbuf, &retval);
#else
    apply_autocmds(EVENT_BUFENTER, NULL, NULL, FALSE, curbuf);
#endif

    if (retval == OK)
    {
	// The autocommands may have changed the current buffer.  Apply the
	// modelines to the correct buffer, if it still exists and is loaded.
	if (bufref_valid(&old_curbuf) && old_curbuf.br_buf->b_ml.ml_mfp != NULL)
	{
	    aco_save_T	aco;

	    // Go to the buffer that was opened.
	    aucmd_prepbuf(&aco, old_curbuf.br_buf);
	    do_modelines(0);
	    curbuf->b_flags &= ~(BF_CHECK_RO | BF_NEVERLOADED);

	    if ((flags & READ_NOWINENTER) == 0)
#ifdef FEAT_EVAL
		apply_autocmds_retval(EVENT_BUFWINENTER, NULL, NULL, FALSE,
							      curbuf, &retval);
#else
		apply_autocmds(EVENT_BUFWINENTER, NULL, NULL, FALSE, curbuf);
#endif

	    // restore curwin/curbuf and a few other things
	    aucmd_restbuf(&aco);
	}
    }

    return retval;
}