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Message-ID: <CAB0TPYHwor85-fWKu+OMT-1ys2L7OSqVoReJRzNOMAE0xK+yzg@mail.gmail.com>
Date: Tue, 12 May 2020 08:46:44 +0200
From: Martijn Coenen <maco@...roid.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Narayan Kamath <narayan@...gle.com>,
Zimuzo Ezeozue <zezeozue@...gle.com>, kernel-team@...roid.com,
Martijn Coenen <maco@...gle.com>,
Bart Van Assche <bvanassche@....org>,
Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
Jaegeuk Kim <jaegeuk@...nel.org>,
linux-block <linux-block@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH v4 10/10] loop: Add LOOP_CONFIGURE ioctl
Hi Jens,
What do you think of this series?
Thanks,
Martijn
On Wed, Apr 29, 2020 at 4:03 PM Martijn Coenen <maco@...roid.com> wrote:
>
> This allows userspace to completely setup a loop device with a single
> ioctl, removing the in-between state where the device can be partially
> configured - eg the loop device has a backing file associated with it,
> but is reading from the wrong offset.
>
> Besides removing the intermediate state, another big benefit of this
> ioctl is that LOOP_SET_STATUS can be 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.
>
> In addition to doing what LOOP_SET_STATUS can do, LOOP_CONFIGURE can
> also be used to:
> - Set the correct block size immediately by setting
> loop_config.block_size (avoids LOOP_SET_BLOCK_SIZE)
> - Explicitly request direct I/O mode by setting LO_FLAGS_DIRECT_IO
> in loop_config.info.lo_flags (avoids LOOP_SET_DIRECT_IO)
> - Explicitly request read-only mode by setting LO_FLAGS_READ_ONLY
> in loop_config.info.lo_flags
>
> Here's setting up ~70 regular loop devices with an offset on an x86
> Android device, using LOOP_SET_FD and LOOP_SET_STATUS:
>
> vsoc_x86:/system/apex # time for i in `seq 30 100`;
> do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
> 0m03.40s real 0m00.02s user 0m00.03s system
>
> Here's configuring ~70 devices in the same way, but using a modified
> losetup that uses the new LOOP_CONFIGURE ioctl:
>
> vsoc_x86:/system/apex # time for i in `seq 30 100`;
> do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
> 0m01.94s real 0m00.01s user 0m00.01s system
>
> Signed-off-by: Martijn Coenen <maco@...roid.com>
> ---
> drivers/block/loop.c | 107 +++++++++++++++++++++++++++-----------
> include/uapi/linux/loop.h | 21 ++++++++
> 2 files changed, 99 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index cfbdd99fdb1a..a353ce55fd18 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -241,6 +241,19 @@ loop_validate_size(loff_t size)
> return 0;
> }
>
> +/**
> + * loop_validate_block_size() - validates the passed in block size
> + * @bsize: size to validate
> + */
> +static int
> +loop_validate_block_size(unsigned short bsize)
> +{
> + if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> /**
> * loop_set_size() - sets device size and notifies userspace
> * @lo: struct loop_device to set the size for
> @@ -1063,23 +1076,24 @@ loop_set_status_from_info(struct loop_device *lo,
> return 0;
> }
>
> -static int loop_set_fd(struct loop_device *lo, fmode_t mode,
> - struct block_device *bdev, unsigned int arg)
> +static int loop_configure(struct loop_device *lo, fmode_t mode,
> + struct block_device *bdev,
> + const struct loop_config *config)
> {
> struct file *file;
> struct inode *inode;
> struct address_space *mapping;
> struct block_device *claimed_bdev = NULL;
> - int lo_flags = 0;
> int error;
> loff_t size;
> bool partscan;
> + unsigned short bsize;
>
> /* This is safe, since we have a reference from open(). */
> __module_get(THIS_MODULE);
>
> error = -EBADF;
> - file = fget(arg);
> + file = fget(config->fd);
> if (!file)
> goto out;
>
> @@ -1088,7 +1102,7 @@ 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_configure);
> if (IS_ERR(claimed_bdev)) {
> error = PTR_ERR(claimed_bdev);
> goto out_putf;
> @@ -1110,44 +1124,58 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
> mapping = file->f_mapping;
> inode = mapping->host;
>
> - if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) ||
> - !file->f_op->write_iter)
> - lo_flags |= LO_FLAGS_READ_ONLY;
> -
> size = get_loop_size(lo, file);
> error = loop_validate_size(size);
> if (error)
> goto out_unlock;
> +
> + if ((config->info.lo_flags & ~LOOP_CONFIGURE_SETTABLE_FLAGS) != 0) {
> + error = -EINVAL;
> + goto out_unlock;
> + }
> +
> + if (config->block_size) {
> + error = loop_validate_block_size(config->block_size);
> + if (error)
> + goto out_unlock;
> + }
> +
> + error = loop_set_status_from_info(lo, &config->info);
> + if (error)
> + goto out_unlock;
> +
> + if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) ||
> + !file->f_op->write_iter)
> + lo->lo_flags |= LO_FLAGS_READ_ONLY;
> +
> error = loop_prepare_queue(lo);
> if (error)
> goto out_unlock;
>
> error = 0;
>
> - set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0);
> + set_device_ro(bdev, (lo->lo_flags & LO_FLAGS_READ_ONLY) != 0);
>
> - lo->use_dio = false;
> + lo->use_dio = lo->lo_flags & LO_FLAGS_DIRECT_IO;
> lo->lo_device = bdev;
> - lo->lo_flags = lo_flags;
> lo->lo_backing_file = file;
> - lo->transfer = NULL;
> - lo->ioctl = NULL;
> - lo->lo_sizelimit = 0;
> lo->old_gfp_mask = mapping_gfp_mask(mapping);
> mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
>
> - if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
> + if (!(lo->lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
> blk_queue_write_cache(lo->lo_queue, true, false);
>
> - if (io_is_direct(lo->lo_backing_file) && inode->i_sb->s_bdev) {
> + if (config->block_size)
> + bsize = config->block_size;
> + else if (io_is_direct(lo->lo_backing_file) && inode->i_sb->s_bdev)
> /* In case of direct I/O, match underlying block size */
> - unsigned short bsize = bdev_logical_block_size(
> - inode->i_sb->s_bdev);
> + bsize = bdev_logical_block_size(inode->i_sb->s_bdev);
> + else
> + bsize = 512;
>
> - blk_queue_logical_block_size(lo->lo_queue, bsize);
> - blk_queue_physical_block_size(lo->lo_queue, bsize);
> - blk_queue_io_min(lo->lo_queue, bsize);
> - }
> + blk_queue_logical_block_size(lo->lo_queue, bsize);
> + blk_queue_physical_block_size(lo->lo_queue, bsize);
> + blk_queue_io_min(lo->lo_queue, bsize);
>
> loop_update_rotational(lo);
> loop_update_dio(lo);
> @@ -1170,14 +1198,14 @@ 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_configure);
> 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_configure);
> out_putf:
> fput(file);
> out:
> @@ -1607,8 +1635,9 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
> if (lo->lo_state != Lo_bound)
> return -ENXIO;
>
> - if (arg < 512 || arg > PAGE_SIZE || !is_power_of_2(arg))
> - return -EINVAL;
> + err = loop_validate_block_size(arg);
> + if (err)
> + return err;
>
> if (lo->lo_queue->limits.logical_block_size == arg)
> return 0;
> @@ -1670,8 +1699,27 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
> int err;
>
> switch (cmd) {
> - case LOOP_SET_FD:
> - return loop_set_fd(lo, mode, bdev, arg);
> + case LOOP_SET_FD: {
> + /*
> + * Legacy case - pass in a zeroed out struct loop_config with
> + * only the file descriptor set , which corresponds with the
> + * default parameters we'd have used otherwise.
> + */
> + struct loop_config config;
> +
> + memset(&config, 0, sizeof(config));
> + config.fd = arg;
> +
> + return loop_configure(lo, mode, bdev, &config);
> + }
> + case LOOP_CONFIGURE: {
> + struct loop_config config;
> +
> + if (copy_from_user(&config, argp, sizeof(config)))
> + return -EFAULT;
> +
> + return loop_configure(lo, mode, bdev, &config);
> + }
> case LOOP_CHANGE_FD:
> return loop_change_fd(lo, bdev, arg);
> case LOOP_CLR_FD:
> @@ -1843,6 +1891,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
> case LOOP_CLR_FD:
> case LOOP_GET_STATUS64:
> case LOOP_SET_STATUS64:
> + case LOOP_CONFIGURE:
> arg = (unsigned long) compat_ptr(arg);
> /* fall through */
> case LOOP_SET_FD:
> diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
> index 6b32fee80ce0..24a1c45bd1ae 100644
> --- a/include/uapi/linux/loop.h
> +++ b/include/uapi/linux/loop.h
> @@ -31,6 +31,10 @@ enum {
> /* LO_FLAGS that can be cleared using LOOP_SET_STATUS(64) */
> #define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR)
>
> +/* LO_FLAGS that can be set using LOOP_CONFIGURE */
> +#define LOOP_CONFIGURE_SETTABLE_FLAGS (LO_FLAGS_READ_ONLY | LO_FLAGS_AUTOCLEAR \
> + | LO_FLAGS_PARTSCAN | LO_FLAGS_DIRECT_IO)
> +
> #include <asm/posix_types.h> /* for __kernel_old_dev_t */
> #include <linux/types.h> /* for __u64 */
>
> @@ -66,6 +70,22 @@ struct loop_info64 {
> __u64 lo_init[2];
> };
>
> +/**
> + * struct loop_config - Complete configuration for a loop device.
> + * @fd: fd of the file to be used as a backing file for the loop device.
> + * @block_size: block size to use; ignored if 0.
> + * @info: struct loop_info64 to configure the loop device with.
> + *
> + * This structure is used with the LOOP_CONFIGURE ioctl, and can be used to
> + * atomically setup and configure all loop device parameters at once.
> + */
> +struct loop_config {
> + __u32 fd;
> + __u32 block_size;
> + struct loop_info64 info;
> + __u64 __reserved[8];
> +};
> +
> /*
> * Loop filter types
> */
> @@ -96,6 +116,7 @@ struct loop_info64 {
> #define LOOP_SET_CAPACITY 0x4C07
> #define LOOP_SET_DIRECT_IO 0x4C08
> #define LOOP_SET_BLOCK_SIZE 0x4C09
> +#define LOOP_CONFIGURE 0x4C0A
>
> /* /dev/loop-control interface */
> #define LOOP_CTL_ADD 0x4C80
> --
> 2.26.2.303.gf8c07b1a785-goog
>
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