From nobody Sun Dec 28 00:48:25 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9C1FE6E2B5 for ; Thu, 14 Dec 2023 21:42:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="zHOemZYY"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="pr25KLwQ" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1702590126; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q48uIAB5AY2ApKCo1murQeJaZPOP9JBGkCMa5H/oZks=; b=zHOemZYYUinMd2+/7z/PQK/1U+igGlMmD7jmxS6Ujm81Or1gMFCOoM+izS3ovWoNVJ97tB uA9ukV2FOOOIUDQytwfsbYIR3+BauWy7FCDYOb5bgi64ehVTu/xqXo5XneymPobzurpnVE RZdwxZJpRAShbTVLBbFRYl7z5KBdCosXmU7FKu4A+V9vqd7EmhzTGAdqSz6Nld579vhFLj nC952Fb91S/HCwroykcAHUWkF4ek1Va1RdTgT42/tMrwnFSmIgR01Y+HQ+aOOL8AlFw+Kd QN/Z9vsLxsAaEnYxLJVRDSzZhLiJ3S6RjQtTnJvA+dMGeDVg739sMfCkW75cxw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1702590126; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q48uIAB5AY2ApKCo1murQeJaZPOP9JBGkCMa5H/oZks=; b=pr25KLwQUYt7bJV24yRRf26QkQaWfQ8a2xyOsOekYXPINKQ2n8GiQESfD07H7wbe+Babal sq/QlnfnnIh5XTBw== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v3 05/14] printk: ringbuffer: Clarify special lpos values Date: Thu, 14 Dec 2023 22:47:52 +0106 Message-Id: <20231214214201.499426-6-john.ogness@linutronix.de> In-Reply-To: <20231214214201.499426-1-john.ogness@linutronix.de> References: <20231214214201.499426-1-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For empty line records, no data blocks are created. Instead, these valid records are identified by special logical position values (in fields of @prb_desc.text_blk_lpos). Currently the macro NO_LPOS is used for empty line records. This name is confusing because it does not imply _why_ there is no data block. Rename NO_LPOS to EMPTY_LINE_LPOS so that it is clear why there is no data block. Also add comments explaining the use of EMPTY_LINE_LPOS as well as clarification to the values used to represent data-less blocks. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- kernel/printk/printk_ringbuffer.c | 20 ++++++++++++++++---- kernel/printk/printk_ringbuffer.h | 16 +++++++++++++++- 2 files changed, 31 insertions(+), 5 deletions(-) diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringb= uffer.c index 04c26cca546f..244d991ffd73 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -1034,9 +1034,13 @@ static char *data_alloc(struct printk_ringbuffer *rb= , unsigned int size, unsigned long next_lpos; =20 if (size =3D=3D 0) { - /* Specify a data-less block. */ - blk_lpos->begin =3D NO_LPOS; - blk_lpos->next =3D NO_LPOS; + /* + * Data blocks are not created for empty lines. Instead, the + * reader will recognize these special lpos values and handle + * it appropriately. + */ + blk_lpos->begin =3D EMPTY_LINE_LPOS; + blk_lpos->next =3D EMPTY_LINE_LPOS; return NULL; } =20 @@ -1214,10 +1218,18 @@ static const char *get_data(struct prb_data_ring *d= ata_ring, =20 /* Data-less data block description. */ if (BLK_DATALESS(blk_lpos)) { - if (blk_lpos->begin =3D=3D NO_LPOS && blk_lpos->next =3D=3D NO_LPOS) { + /* + * Records that are just empty lines are also valid, even + * though they do not have a data block. For such records + * explicitly return empty string data to signify success. + */ + if (blk_lpos->begin =3D=3D EMPTY_LINE_LPOS && + blk_lpos->next =3D=3D EMPTY_LINE_LPOS) { *data_size =3D 0; return ""; } + + /* Data lost, invalid, or otherwise unavailable. */ return NULL; } =20 diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringb= uffer.h index 2d948cc82b5b..d49460f7578e 100644 --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -127,8 +127,22 @@ enum desc_state { #define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | i= d) #define DESC_ID_MASK (~DESC_FLAGS_MASK) #define DESC_ID(sv) ((sv) & DESC_ID_MASK) + +/* + * Special data block logical position values (for fields of + * @prb_desc.text_blk_lpos). + * + * - Bit0 is used to identify if the record has no data block. (Implemente= d in + * the LPOS_DATALESS() macro.) + * + * - Bit1 specifies the reason for not having a data block. + * + * These special values could never be real lpos values because of the + * meta data and alignment padding of data blocks. (See to_blk_size() for + * details.) + */ #define FAILED_LPOS 0x1 -#define NO_LPOS 0x3 +#define EMPTY_LINE_LPOS 0x3 =20 #define FAILED_BLK_LPOS \ { \ --=20 2.39.2