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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09437C4363C for ; Wed, 7 Oct 2020 07:55:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 921D8207EA for ; Wed, 7 Oct 2020 07:55:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727832AbgJGHzk (ORCPT ); Wed, 7 Oct 2020 03:55:40 -0400 Received: from verein.lst.de ([213.95.11.211]:36491 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727647AbgJGHzk (ORCPT ); Wed, 7 Oct 2020 03:55:40 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 4280D6736F; Wed, 7 Oct 2020 09:55:37 +0200 (CEST) Date: Wed, 7 Oct 2020 09:55:37 +0200 From: Christoph Hellwig To: Kees Cook Cc: Christoph Hellwig , WeiXiong Liao , linux-kernel@vger.kernel.org Subject: Re: use case for register_pstore_blk? Message-ID: <20201007075537.GA12531@lst.de> References: <20201006155220.GA11668@lst.de> <202010070007.8FF59EC42@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202010070007.8FF59EC42@keescook> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2020 at 12:13:27AM -0700, Kees Cook wrote: > On Tue, Oct 06, 2020 at 05:52:20PM +0200, Christoph Hellwig wrote: > > Hi WeiXiong, hi Kees, > > > > what is the use case for the code added in commit 17639f67c1d6 > > ("pstore/blk: Introduce backend for block devices"). > > > > This still doesn't have a user, and the API looks really odd to me. > > pstore is a beast. :) The API is there so that a blk device can declare > its direct support of pstore (specifically, to provide a panic_write > handler). > > The MTD device does this, but yes, that's a good point, there isn't a > blk device user of that entry point yet. > > > By our normal kernel rules we should not add new exports without > > users and this should probably be reverted for the 5.9 release. > > I don't want to revert the entire patch (I'm still using > __register_pstore_blk by way of pstore/blk's "best_effort" option), but > I wouldn't object to something like this: FYI, I'd be much happier with this, which removes the crazy block device autoprobe, and the completely broken block device read/write path as well: diff --git a/Documentation/admin-guide/pstore-blk.rst b/Documentation/admin-guide/pstore-blk.rst index 296d5027787ac2..84d15c53d094c0 100644 --- a/Documentation/admin-guide/pstore-blk.rst +++ b/Documentation/admin-guide/pstore-blk.rst @@ -151,13 +151,7 @@ otherwise KMSG_DUMP_MAX. Configurations for driver ------------------------- -Only a block device driver cares about these configurations. A block device -driver uses ``register_pstore_blk`` to register to pstore/blk. - -.. kernel-doc:: fs/pstore/blk.c - :identifiers: register_pstore_blk - -A non-block device driver uses ``register_pstore_device`` with +Device drivers use ``register_pstore_device`` with ``struct pstore_device_info`` to register to pstore/blk. .. kernel-doc:: fs/pstore/blk.c diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c index fcd5563dde063c..3a8224c6df24f5 100644 --- a/fs/pstore/blk.c +++ b/fs/pstore/blk.c @@ -88,15 +88,7 @@ MODULE_PARM_DESC(blkdev, "block device for pstore storage"); * during the register/unregister functions. */ static DEFINE_MUTEX(pstore_blk_lock); -static struct block_device *psblk_bdev; static struct pstore_zone_info *pstore_zone_info; -static pstore_blk_panic_write_op blkdev_panic_write; - -struct bdev_info { - dev_t devt; - sector_t nr_sects; - sector_t start_sect; -}; #define check_size(name, alignsize) ({ \ long _##name_ = (name); \ @@ -206,267 +198,6 @@ void unregister_pstore_device(struct pstore_device_info *dev) } EXPORT_SYMBOL_GPL(unregister_pstore_device); -/** - * psblk_get_bdev() - open block device - * - * @holder: Exclusive holder identifier - * @info: Information about bdev to fill in - * - * Return: pointer to block device on success and others on error. - * - * On success, the returned block_device has reference count of one. - */ -static struct block_device *psblk_get_bdev(void *holder, - struct bdev_info *info) -{ - struct block_device *bdev = ERR_PTR(-ENODEV); - fmode_t mode = FMODE_READ | FMODE_WRITE; - sector_t nr_sects; - - lockdep_assert_held(&pstore_blk_lock); - - if (pstore_zone_info) - return ERR_PTR(-EBUSY); - - if (!blkdev[0]) - return ERR_PTR(-ENODEV); - - if (holder) - mode |= FMODE_EXCL; - bdev = blkdev_get_by_path(blkdev, mode, holder); - if (IS_ERR(bdev)) { - dev_t devt; - - devt = name_to_dev_t(blkdev); - if (devt == 0) - return ERR_PTR(-ENODEV); - bdev = blkdev_get_by_dev(devt, mode, holder); - if (IS_ERR(bdev)) - return bdev; - } - - nr_sects = part_nr_sects_read(bdev->bd_part); - if (!nr_sects) { - pr_err("not enough space for '%s'\n", blkdev); - blkdev_put(bdev, mode); - return ERR_PTR(-ENOSPC); - } - - if (info) { - info->devt = bdev->bd_dev; - info->nr_sects = nr_sects; - info->start_sect = get_start_sect(bdev); - } - - return bdev; -} - -static void psblk_put_bdev(struct block_device *bdev, void *holder) -{ - fmode_t mode = FMODE_READ | FMODE_WRITE; - - lockdep_assert_held(&pstore_blk_lock); - - if (!bdev) - return; - - if (holder) - mode |= FMODE_EXCL; - blkdev_put(bdev, mode); -} - -static ssize_t psblk_generic_blk_read(char *buf, size_t bytes, loff_t pos) -{ - struct block_device *bdev = psblk_bdev; - struct file file; - struct kiocb kiocb; - struct iov_iter iter; - struct kvec iov = {.iov_base = buf, .iov_len = bytes}; - - if (!bdev) - return -ENODEV; - - memset(&file, 0, sizeof(struct file)); - file.f_mapping = bdev->bd_inode->i_mapping; - file.f_flags = O_DSYNC | __O_SYNC | O_NOATIME; - file.f_inode = bdev->bd_inode; - file_ra_state_init(&file.f_ra, file.f_mapping); - - init_sync_kiocb(&kiocb, &file); - kiocb.ki_pos = pos; - iov_iter_kvec(&iter, READ, &iov, 1, bytes); - - return generic_file_read_iter(&kiocb, &iter); -} - -static ssize_t psblk_generic_blk_write(const char *buf, size_t bytes, - loff_t pos) -{ - struct block_device *bdev = psblk_bdev; - struct iov_iter iter; - struct kiocb kiocb; - struct file file; - ssize_t ret; - struct kvec iov = {.iov_base = (void *)buf, .iov_len = bytes}; - - if (!bdev) - return -ENODEV; - - /* Console/Ftrace backend may handle buffer until flush dirty zones */ - if (in_interrupt() || irqs_disabled()) - return -EBUSY; - - memset(&file, 0, sizeof(struct file)); - file.f_mapping = bdev->bd_inode->i_mapping; - file.f_flags = O_DSYNC | __O_SYNC | O_NOATIME; - file.f_inode = bdev->bd_inode; - - init_sync_kiocb(&kiocb, &file); - kiocb.ki_pos = pos; - iov_iter_kvec(&iter, WRITE, &iov, 1, bytes); - - inode_lock(bdev->bd_inode); - ret = generic_write_checks(&kiocb, &iter); - if (ret > 0) - ret = generic_perform_write(&file, &iter, pos); - inode_unlock(bdev->bd_inode); - - if (likely(ret > 0)) { - const struct file_operations f_op = {.fsync = blkdev_fsync}; - - file.f_op = &f_op; - kiocb.ki_pos += ret; - ret = generic_write_sync(&kiocb, ret); - } - return ret; -} - -static ssize_t psblk_blk_panic_write(const char *buf, size_t size, - loff_t off) -{ - int ret; - - if (!blkdev_panic_write) - return -EOPNOTSUPP; - - /* size and off must align to SECTOR_SIZE for block device */ - ret = blkdev_panic_write(buf, off >> SECTOR_SHIFT, - size >> SECTOR_SHIFT); - /* try next zone */ - if (ret == -ENOMSG) - return ret; - return ret ? -EIO : size; -} - -static int __register_pstore_blk(struct pstore_blk_info *info) -{ - char bdev_name[BDEVNAME_SIZE]; - struct block_device *bdev; - struct pstore_device_info dev; - struct bdev_info binfo; - void *holder = blkdev; - int ret = -ENODEV; - - lockdep_assert_held(&pstore_blk_lock); - - /* hold bdev exclusively */ - memset(&binfo, 0, sizeof(binfo)); - bdev = psblk_get_bdev(holder, &binfo); - if (IS_ERR(bdev)) { - pr_err("failed to open '%s'!\n", blkdev); - return PTR_ERR(bdev); - } - - /* only allow driver matching the @blkdev */ - if (!binfo.devt || (!best_effort && - MAJOR(binfo.devt) != info->major)) { - pr_debug("invalid major %u (expect %u)\n", - info->major, MAJOR(binfo.devt)); - ret = -ENODEV; - goto err_put_bdev; - } - - /* psblk_bdev must be assigned before register to pstore/blk */ - psblk_bdev = bdev; - blkdev_panic_write = info->panic_write; - - /* Copy back block device details. */ - info->devt = binfo.devt; - info->nr_sects = binfo.nr_sects; - info->start_sect = binfo.start_sect; - - memset(&dev, 0, sizeof(dev)); - dev.total_size = info->nr_sects << SECTOR_SHIFT; - dev.flags = info->flags; - dev.read = psblk_generic_blk_read; - dev.write = psblk_generic_blk_write; - dev.erase = NULL; - dev.panic_write = info->panic_write ? psblk_blk_panic_write : NULL; - - ret = __register_pstore_device(&dev); - if (ret) - goto err_put_bdev; - - bdevname(bdev, bdev_name); - pr_info("attached %s%s\n", bdev_name, - info->panic_write ? "" : " (no dedicated panic_write!)"); - return 0; - -err_put_bdev: - psblk_bdev = NULL; - blkdev_panic_write = NULL; - psblk_put_bdev(bdev, holder); - return ret; -} - -/** - * register_pstore_blk() - register block device to pstore/blk - * - * @info: details on the desired block device interface - * - * Return: - * * 0 - OK - * * Others - something error. - */ -int register_pstore_blk(struct pstore_blk_info *info) -{ - int ret; - - mutex_lock(&pstore_blk_lock); - ret = __register_pstore_blk(info); - mutex_unlock(&pstore_blk_lock); - - return ret; -} -EXPORT_SYMBOL_GPL(register_pstore_blk); - -static void __unregister_pstore_blk(unsigned int major) -{ - struct pstore_device_info dev = { .read = psblk_generic_blk_read }; - void *holder = blkdev; - - lockdep_assert_held(&pstore_blk_lock); - if (psblk_bdev && MAJOR(psblk_bdev->bd_dev) == major) { - __unregister_pstore_device(&dev); - psblk_put_bdev(psblk_bdev, holder); - blkdev_panic_write = NULL; - psblk_bdev = NULL; - } -} - -/** - * unregister_pstore_blk() - unregister block device from pstore/blk - * - * @major: the major device number of device - */ -void unregister_pstore_blk(unsigned int major) -{ - mutex_lock(&pstore_blk_lock); - __unregister_pstore_blk(major); - mutex_unlock(&pstore_blk_lock); -} -EXPORT_SYMBOL_GPL(unregister_pstore_blk); - /* get information of pstore/blk */ int pstore_blk_get_config(struct pstore_blk_config *info) { @@ -481,32 +212,14 @@ int pstore_blk_get_config(struct pstore_blk_config *info) } EXPORT_SYMBOL_GPL(pstore_blk_get_config); -static int __init pstore_blk_init(void) -{ - struct pstore_blk_info info = { }; - int ret = 0; - - mutex_lock(&pstore_blk_lock); - if (!pstore_zone_info && best_effort && blkdev[0]) - ret = __register_pstore_blk(&info); - mutex_unlock(&pstore_blk_lock); - - return ret; -} -late_initcall(pstore_blk_init); - static void __exit pstore_blk_exit(void) { - mutex_lock(&pstore_blk_lock); - if (psblk_bdev) - __unregister_pstore_blk(MAJOR(psblk_bdev->bd_dev)); - else { - struct pstore_device_info dev = { }; + struct pstore_device_info dev = { }; - if (pstore_zone_info) - dev.read = pstore_zone_info->read; - __unregister_pstore_device(&dev); - } + mutex_lock(&pstore_blk_lock); + if (pstore_zone_info) + dev.read = pstore_zone_info->read; + __unregister_pstore_device(&dev); mutex_unlock(&pstore_blk_lock); } module_exit(pstore_blk_exit); diff --git a/include/linux/pstore_blk.h b/include/linux/pstore_blk.h index 61e914522b0193..9a9bf76ea73960 100644 --- a/include/linux/pstore_blk.h +++ b/include/linux/pstore_blk.h @@ -22,33 +22,6 @@ typedef int (*pstore_blk_panic_write_op)(const char *buf, sector_t start_sect, sector_t sects); -/** - * struct pstore_blk_info - pstore/blk registration details - * - * @major: Which major device number to support with pstore/blk - * @flags: The supported PSTORE_FLAGS_* from linux/pstore.h. - * @panic_write:The write operation only used for the panic case. - * This can be NULL, but is recommended to avoid losing - * crash data if the kernel's IO path or work queues are - * broken during a panic. - * @devt: The dev_t that pstore/blk has attached to. - * @nr_sects: Number of sectors on @devt. - * @start_sect: Starting sector on @devt. - */ -struct pstore_blk_info { - unsigned int major; - unsigned int flags; - pstore_blk_panic_write_op panic_write; - - /* Filled in by pstore/blk after registration. */ - dev_t devt; - sector_t nr_sects; - sector_t start_sect; -}; - -int register_pstore_blk(struct pstore_blk_info *info); -void unregister_pstore_blk(unsigned int major); - /** * struct pstore_device_info - back-end pstore/blk driver structure. *