From patchwork Tue Mar 31 11:40:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Martijn Coenen X-Patchwork-Id: 11467627 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 543BF92C for ; Tue, 31 Mar 2020 11:40:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2853320838 for ; Tue, 31 Mar 2020 11:40:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=android.com header.i=@android.com header.b="ZJ89ys9x" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730418AbgCaLkh (ORCPT ); Tue, 31 Mar 2020 07:40:37 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:37379 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729483AbgCaLkh (ORCPT ); Tue, 31 Mar 2020 07:40:37 -0400 Received: by mail-wr1-f67.google.com with SMTP id w10so25561724wrm.4 for ; Tue, 31 Mar 2020 04:40:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=android.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=KksWWx9+HSMSD+6b37njirIFwS8trrPXD/rr78+IGUc=; b=ZJ89ys9xS3z8+VcSl6yH6jpNCecRSQQRuFpHgXGlpfBT7YOsAagDhi5IkrZ72P6h/G zhldGY0MxWCmjoidCg5z5i8KvX982raeYdxtooozR5RxbM93T/aLSuxu5/h+mDIProVL 4+isSb0f2pqjpB/Uj8LWAjHyWAFRTaCxeQ6NYZoU3hzBaN/NsZ8ZrTETEjhOZlBeStQF pQn79HBH/sZLh0wPsnF4XL2NZN1Qql9et0szt+Fac2nqdujOqHeMI1EtHql4dQlYIOC2 9v8WYawCtncRICFcP4POI0cvcIIkcthu0AsmeW0KeK6puB0pTiDpSzg9PIP+Gu+eMZZm U06Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=KksWWx9+HSMSD+6b37njirIFwS8trrPXD/rr78+IGUc=; b=YUrCK3Wz1JMYjUAF09BObhXOVSTsU+5o7UjD/PcfDGSwqajTecK05nQsVZc2KC8jiJ 0LWLEeTFdX9BhDX4UU2yd3cNQIcIW+QSHXs8TiySkY7/gxKMCB99npD1SQNb4smvEv4T YKSJrtG5pOot5KfcH/yowMHztCF09KWrNJhxGajJfhyivXjwCm3hJQUr4rrTGC3SHOIr FRZCDpgypJzuI2+3GFWZJDE3gOPXkpJuHd7pH5kb/S0QqdbzSOfxe0b/1URU7EEh9/dg atql71v+SDpPHfcIxvWvK6e1mCxrr9HrasJ3rBZ/jQp65dL5xbxCWvzmp2QUe+hUsF3y OpzQ== X-Gm-Message-State: ANhLgQ1ZPV4iambO25/izWHLCNSDxCR4tjUiGQOivrkjjNMMBJKGu2/C yyGlpumh6ASb3tLlRvZmgQPiTg== X-Google-Smtp-Source: ADFU+vtiasCfBsInULXJsE5MWNQJVLIt0XVrCsw1CS2ZQtPKly0an4ydEtLmrh6/+fhXbCAtlkJHIQ== X-Received: by 2002:adf:b307:: with SMTP id j7mr21020303wrd.128.1585654835319; Tue, 31 Mar 2020 04:40:35 -0700 (PDT) Received: from maco2.ams.corp.google.com (a83-162-234-235.adsl.xs4all.nl. [83.162.234.235]) by smtp.gmail.com with ESMTPSA id w7sm26035307wrr.60.2020.03.31.04.40.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 04:40:34 -0700 (PDT) From: Martijn Coenen To: axboe@kernel.dk, hch@lst.de Cc: ming.lei@redhat.com, bvanassche@acm.org, Chaitanya.Kulkarni@wdc.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com, Martijn Coenen Subject: [PATCH] loop: Add LOOP_SET_FD_WITH_OFFSET ioctl. Date: Tue, 31 Mar 2020 13:40:30 +0200 Message-Id: <20200331114030.21262-1-maco@android.com> X-Mailer: git-send-email 2.26.0.rc2.310.g2932bb562d-goog MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Configuring a loop device for a filesystem that is located at an offset currently requires calling LOOP_SET_FD and LOOP_SET_STATUS(64) consecutively. This has some downsides. The most important downside is that it can be slow. Here's setting up ~70 regular loop devices on an x86 Android device: vsoc_x86:/system/apex # time for i in `seq 30 100`; do losetup -r /dev/block/loop$i com.android.adbd.apex; done 0m01.85s real 0m00.01s user 0m00.01s system Here's configuring ~70 devices in the same way, but with an offset: vsoc_x86:/system/apex # time for i in `seq 30 100`; do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done 0m03.40s real 0m00.02s user 0m00.03s system This is almost twice as slow; the main reason for this slowness is that LOOP_SET_STATUS(64) calls blk_mq_freeze_queue() to freeze the associated queue; this requires waiting for RCU synchronization, which I've measured can take about 15-20ms on this device on average. A more minor downside of having to do two ioctls is that on devices with max_part > 0, the kernel will initiate a partition scan, which is needless work if the image is at an offset. This change introduces a new ioctl to combine setting the backing file together with the offset, which avoids the above problems. Adding more parameters could be a consideration, but offset appears to be the only commonly used parameter that is required for accessing the device safely. Signed-off-by: Martijn Coenen --- drivers/block/loop.c | 25 +++++++++++++++++++------ include/uapi/linux/loop.h | 6 ++++++ 2 files changed, 25 insertions(+), 6 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index a42c49e04954..517031e1d10c 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -932,8 +932,8 @@ static void loop_update_rotational(struct loop_device *lo) blk_queue_flag_clear(QUEUE_FLAG_NONROT, q); } -static int loop_set_fd(struct loop_device *lo, fmode_t mode, - struct block_device *bdev, unsigned int arg) +static int loop_set_fd_with_offset(struct loop_device *lo, fmode_t mode, + struct block_device *bdev, unsigned int arg, loff_t offset) { struct file *file; struct inode *inode; @@ -957,7 +957,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, * here to avoid changing device under exclusive owner. */ if (!(mode & FMODE_EXCL)) { - claimed_bdev = bd_start_claiming(bdev, loop_set_fd); + claimed_bdev = bd_start_claiming(bdev, loop_set_fd_with_offset); if (IS_ERR(claimed_bdev)) { error = PTR_ERR(claimed_bdev); goto out_putf; @@ -1002,6 +1002,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, lo->transfer = NULL; lo->ioctl = NULL; lo->lo_sizelimit = 0; + lo->lo_offset = offset; lo->old_gfp_mask = mapping_gfp_mask(mapping); mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS)); @@ -1042,14 +1043,14 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, if (partscan) loop_reread_partitions(lo, bdev); if (claimed_bdev) - bd_abort_claiming(bdev, claimed_bdev, loop_set_fd); + bd_abort_claiming(bdev, claimed_bdev, loop_set_fd_with_offset); return 0; out_unlock: mutex_unlock(&loop_ctl_mutex); out_bdev: if (claimed_bdev) - bd_abort_claiming(bdev, claimed_bdev, loop_set_fd); + bd_abort_claiming(bdev, claimed_bdev, loop_set_fd_with_offset); out_putf: fput(file); out: @@ -1601,7 +1602,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, switch (cmd) { case LOOP_SET_FD: - return loop_set_fd(lo, mode, bdev, arg); + return loop_set_fd_with_offset(lo, mode, bdev, arg, 0); case LOOP_CHANGE_FD: return loop_change_fd(lo, bdev, arg); case LOOP_CLR_FD: @@ -1624,6 +1625,17 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, break; case LOOP_GET_STATUS64: return loop_get_status64(lo, (struct loop_info64 __user *) arg); + case LOOP_SET_FD_WITH_OFFSET: { + struct loop_fd_with_offset fdwo; + + if (copy_from_user(&fdwo, + (struct loop_fd_with_offset __user *) arg, + sizeof(struct loop_fd_with_offset))) + return -EFAULT; + + return loop_set_fd_with_offset(lo, mode, bdev, fdwo.fd, + fdwo.lo_offset); + } case LOOP_SET_CAPACITY: case LOOP_SET_DIRECT_IO: case LOOP_SET_BLOCK_SIZE: @@ -1774,6 +1786,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, case LOOP_SET_CAPACITY: case LOOP_CLR_FD: case LOOP_GET_STATUS64: + case LOOP_SET_FD_WITH_OFFSET: case LOOP_SET_STATUS64: arg = (unsigned long) compat_ptr(arg); /* fall through */ diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h index 080a8df134ef..289829bc5abd 100644 --- a/include/uapi/linux/loop.h +++ b/include/uapi/linux/loop.h @@ -60,6 +60,11 @@ struct loop_info64 { __u64 lo_init[2]; }; +struct loop_fd_with_offset { + __u64 lo_offset; + __u32 fd; +}; + /* * Loop filter types */ @@ -90,6 +95,7 @@ struct loop_info64 { #define LOOP_SET_CAPACITY 0x4C07 #define LOOP_SET_DIRECT_IO 0x4C08 #define LOOP_SET_BLOCK_SIZE 0x4C09 +#define LOOP_SET_FD_WITH_OFFSET 0x4C0A /* /dev/loop-control interface */ #define LOOP_CTL_ADD 0x4C80