From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B2F47C43334 for ; Mon, 20 Jun 2022 04:44:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237672AbiFTEoT convert rfc822-to-8bit (ORCPT ); Mon, 20 Jun 2022 00:44:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229908AbiFTEoR (ORCPT ); Mon, 20 Jun 2022 00:44:17 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 33501A446 for ; Sun, 19 Jun 2022 21:44:16 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-166-e-ku6nOkPGGi772ICmkLdQ-1; Mon, 20 Jun 2022 05:44:13 +0100 X-MC-Unique: e-ku6nOkPGGi772ICmkLdQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.36; Mon, 20 Jun 2022 05:44:10 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.036; Mon, 20 Jun 2022 05:44:10 +0100 From: David Laight To: 'Kent Overstreet' , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "pmladek@suse.com" CC: "rostedt@goodmis.org" , "enozhatsky@chromium.org" , "linux@rasmusvillemoes.dk" , "willy@infradead.org" Subject: RE: [PATCH v4 01/34] lib/printbuf: New data structure for printing strings Thread-Topic: [PATCH v4 01/34] lib/printbuf: New data structure for printing strings Thread-Index: AQHYhD6p9ckAsWkCSk+0B0i5FtmPu61XsWog Date: Mon, 20 Jun 2022 04:44:10 +0000 Message-ID: References: <20220620004233.3805-1-kent.overstreet@gmail.com> <20220620004233.3805-2-kent.overstreet@gmail.com> In-Reply-To: <20220620004233.3805-2-kent.overstreet@gmail.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kent Overstreet > Sent: 20 June 2022 01:42 > > This adds printbufs: a printbuf points to a char * buffer and knows the > size of the output buffer as well as the current output position. > > Future patches will be adding more features to printbuf, but initially > printbufs are targeted at refactoring and improving our existing code in > lib/vsprintf.c - so this initial printbuf patch has the features > required for that. > > Signed-off-by: Kent Overstreet > Reviewed-by: Matthew Wilcox (Oracle) > --- > include/linux/printbuf.h | 122 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 122 insertions(+) > create mode 100644 include/linux/printbuf.h > > diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h > new file mode 100644 > index 0000000000..8186c447ca > --- /dev/null > +++ b/include/linux/printbuf.h > @@ -0,0 +1,122 @@ > +/* SPDX-License-Identifier: LGPL-2.1+ */ > +/* Copyright (C) 2022 Kent Overstreet */ > + > +#ifndef _LINUX_PRINTBUF_H > +#define _LINUX_PRINTBUF_H > + > +#include > +#include > + > +/* > + * Printbufs: String buffer for outputting (printing) to, for vsnprintf > + */ > + > +struct printbuf { > + char *buf; > + unsigned size; > + unsigned pos; No naked unsigneds. > +}; > + > +/* > + * Returns size remaining of output buffer: > + */ > +static inline unsigned printbuf_remaining_size(struct printbuf *out) > +{ > + return out->pos < out->size ? out->size - out->pos : 0; > +} > + > +/* > + * Returns number of characters we can print to the output buffer - i.e. > + * excluding the terminating nul: > + */ > +static inline unsigned printbuf_remaining(struct printbuf *out) > +{ > + return out->pos < out->size ? out->size - out->pos - 1 : 0; > +} Those two are so similar mistakes will be make. You can also just return negatives when the buffer has overlowed and get the callers to test < or <= as required. I also wonder it is necessary to count the total length when the buffer isn't long enough? Unless there is a real pressing need for it I'd not bother. Setting pos == size (after writing the '\0') allows overflow be detected without most of the dangers. > + > +static inline unsigned printbuf_written(struct printbuf *out) > +{ > + return min(out->pos, out->size); That excludes the '\0' for short buffers but includes it for overlong ones. > +} > + > +/* > + * Returns true if output was truncated: > + */ > +static inline bool printbuf_overflowed(struct printbuf *out) > +{ > + return out->pos >= out->size; > +} > + > +static inline void printbuf_nul_terminate(struct printbuf *out) > +{ > + if (out->pos < out->size) > + out->buf[out->pos] = 0; > + else if (out->size) > + out->buf[out->size - 1] = 0; > +} > + > +static inline void __prt_char(struct printbuf *out, char c) > +{ > + if (printbuf_remaining(out)) > + out->buf[out->pos] = c; At this point it is (should be) always safe to add the '\0'. Doing so would save the extra conditionals later on. > + out->pos++; > +} > + > +static inline void prt_char(struct printbuf *out, char c) > +{ > + __prt_char(out, c); > + printbuf_nul_terminate(out); > +} > + > +static inline void __prt_chars(struct printbuf *out, char c, unsigned n) > +{ > + unsigned i, can_print = min(n, printbuf_remaining(out)); > + > + for (i = 0; i < can_print; i++) > + out->buf[out->pos++] = c; > + out->pos += n - can_print; > +} > + > +static inline void prt_chars(struct printbuf *out, char c, unsigned n) > +{ > + __prt_chars(out, c, n); > + printbuf_nul_terminate(out); > +} > + > +static inline void prt_bytes(struct printbuf *out, const void *b, unsigned n) > +{ > + unsigned i, can_print = min(n, printbuf_remaining(out)); > + > + for (i = 0; i < can_print; i++) > + out->buf[out->pos++] = ((char *) b)[i]; > + out->pos += n - can_print; > + > + printbuf_nul_terminate(out); jeepers - that can be written so much better. Something like: unsigned int i, pos = out->pos; int space = pos - out->size - 1; char *tgt = out->buf + pos; const char *src = b; out->pos = pos + n; if (space <= 0) return; if (n > space) n = space; for (i = 0; i < n; i++) tgt[i] = src[i]; tgt[1] = 0; > +} > + > +static inline void prt_str(struct printbuf *out, const char *str) > +{ > + prt_bytes(out, str, strlen(str)); Do you really need to call strlen() and then process the buffer byte by byte? David > +} > + > +static inline void prt_hex_byte(struct printbuf *out, u8 byte) > +{ > + __prt_char(out, hex_asc_hi(byte)); > + __prt_char(out, hex_asc_lo(byte)); > + printbuf_nul_terminate(out); > +} > + > +static inline void prt_hex_byte_upper(struct printbuf *out, u8 byte) > +{ > + __prt_char(out, hex_asc_upper_hi(byte)); > + __prt_char(out, hex_asc_upper_lo(byte)); > + printbuf_nul_terminate(out); > +} > + > +#define PRINTBUF_EXTERN(_buf, _size) \ > +((struct printbuf) { \ > + .buf = _buf, \ > + .size = _size, \ > +}) > + > +#endif /* _LINUX_PRINTBUF_H */ > -- > 2.36.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)