Jens, any concerns the new block device ioctls?
On Sun, Nov 8, 2015 at 11:28 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> If an application wants exclusive access to all of the persistent memory
> provided by an NVDIMM namespace it can use this raw-block-dax facility
> to forgo establishing a filesystem. This capability is targeted
> primarily to hypervisors wanting to provision persistent memory for
> guests. It can be disabled / enabled dynamically via the new BLKDAXSET
> ioctl.
>
> Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> block/ioctl.c | 60 +++++++++++++++++++++++++++++++
> fs/block_dev.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++-
> include/linux/fs.h | 3 ++
> include/uapi/linux/fs.h | 2 +
> 4 files changed, 154 insertions(+), 1 deletion(-)
>
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 8061eba42887..604438f36ddd 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -295,6 +295,52 @@ static inline int is_unrecognized_ioctl(int ret)
> ret == -ENOIOCTLCMD;
> }
>
> +#ifdef CONFIG_FS_DAX
> +static bool blkdev_dax_capable(struct block_device *bdev)
> +{
> + struct gendisk *disk = bdev->bd_disk;
> +
> + if (!disk->fops->direct_access)
> + return false;
> +
> + /*
> + * If the partition is not aligned on a page boundary, we can't
> + * do dax I/O to it.
> + */
> + if ((bdev->bd_part->start_sect % (PAGE_SIZE / 512))
> + || (bdev->bd_part->nr_sects % (PAGE_SIZE / 512)))
> + return false;
> +
> + return true;
> +}
> +
> +static int blkdev_set_dax(struct block_device *bdev, int n)
> +{
> + int rc = 0;
> +
> + if (n)
> + n = S_DAX;
> +
> + if (n && !blkdev_dax_capable(bdev))
> + return -ENOTTY;
> +
> + mutex_lock(&bdev->bd_inode->i_mutex);
> + if (bdev->bd_map_count == 0)
> + inode_set_flags(bdev->bd_inode, n, S_DAX);
> + else
> + rc = -EBUSY;
> + mutex_unlock(&bdev->bd_inode->i_mutex);
> + return rc;
> +}
> +#else
> +static int blkdev_set_dax(struct block_device *bdev, int n)
> +{
> + if (n)
> + return -ENOTTY;
> + return 0;
> +}
> +#endif
> +
> /*
> * always keep this in sync with compat_blkdev_ioctl()
> */
> @@ -449,6 +495,20 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
> case BLKTRACETEARDOWN:
> ret = blk_trace_ioctl(bdev, cmd, (char __user *) arg);
> break;
> + case BLKDAXSET:
> + if (!capable(CAP_SYS_ADMIN))
> + return -EACCES;
> +
> + if (get_user(n, (int __user *)(arg)))
> + return -EFAULT;
> + n = !!n;
> + if (n == !!(bdev->bd_inode->i_flags & S_DAX))
> + return 0;
> +
> + return blkdev_set_dax(bdev, n);
> + case BLKDAXGET:
> + return put_int(arg, !!(bdev->bd_inode->i_flags & S_DAX));
> + break;
> default:
> ret = __blkdev_driver_ioctl(bdev, mode, cmd, arg);
> }
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index d3820f6418c8..09d10667cc19 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1687,13 +1687,101 @@ static const struct address_space_operations def_blk_aops = {
> .is_dirty_writeback = buffer_check_dirty_writeback,
> };
>
> +#ifdef CONFIG_FS_DAX
> +/*
> + * In the raw block case we do not need to contend with truncation nor
> + * unwritten file extents. Without those concerns there is no need for
> + * additional locking beyond the mmap_sem context that these routines
> + * are already executing under.
> + *
> + * Note, there is no protection if the block device is dynamically
> + * resized (partition grow/shrink) during a fault. A stable block device
> + * size is already not enforced in the blkdev_direct_IO path.
> + *
> + * For DAX, it is the responsibility of the block device driver to
> + * ensure the whole-disk device size is stable while requests are in
> + * flight.
> + *
> + * Finally, unlike the filemap_page_mkwrite() case there is no
> + * filesystem superblock to sync against freezing. We still include a
> + * pfn_mkwrite callback for dax drivers to receive write fault
> + * notifications.
> + */
> +static int blkdev_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + return __dax_fault(vma, vmf, blkdev_get_block, NULL);
> +}
> +
> +static int blkdev_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> + pmd_t *pmd, unsigned int flags)
> +{
> + return __dax_pmd_fault(vma, addr, pmd, flags, blkdev_get_block, NULL);
> +}
> +
> +static void blkdev_vm_open(struct vm_area_struct *vma)
> +{
> + struct inode *bd_inode = bdev_file_inode(vma->vm_file);
> + struct block_device *bdev = I_BDEV(bd_inode);
> +
> + mutex_lock(&bd_inode->i_mutex);
> + bdev->bd_map_count++;
> + mutex_unlock(&bd_inode->i_mutex);
> +}
> +
> +static void blkdev_vm_close(struct vm_area_struct *vma)
> +{
> + struct inode *bd_inode = bdev_file_inode(vma->vm_file);
> + struct block_device *bdev = I_BDEV(bd_inode);
> +
> + mutex_lock(&bd_inode->i_mutex);
> + bdev->bd_map_count--;
> + mutex_unlock(&bd_inode->i_mutex);
> +}
> +
> +static const struct vm_operations_struct blkdev_dax_vm_ops = {
> + .open = blkdev_vm_open,
> + .close = blkdev_vm_close,
> + .fault = blkdev_dax_fault,
> + .pmd_fault = blkdev_dax_pmd_fault,
> + .pfn_mkwrite = blkdev_dax_fault,
> +};
> +
> +static const struct vm_operations_struct blkdev_default_vm_ops = {
> + .open = blkdev_vm_open,
> + .close = blkdev_vm_close,
> + .fault = filemap_fault,
> + .map_pages = filemap_map_pages,
> +};
> +
> +static int blkdev_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct inode *bd_inode = bdev_file_inode(file);
> + struct block_device *bdev = I_BDEV(bd_inode);
> +
> + file_accessed(file);
> + mutex_lock(&bd_inode->i_mutex);
> + bdev->bd_map_count++;
> + if (IS_DAX(bd_inode)) {
> + vma->vm_ops = &blkdev_dax_vm_ops;
> + vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
> + } else {
> + vma->vm_ops = &blkdev_default_vm_ops;
> + }
> + mutex_unlock(&bd_inode->i_mutex);
> +
> + return 0;
> +}
> +#else
> +#define blkdev_mmap generic_file_mmap
> +#endif
> +
> const struct file_operations def_blk_fops = {
> .open = blkdev_open,
> .release = blkdev_close,
> .llseek = block_llseek,
> .read_iter = blkdev_read_iter,
> .write_iter = blkdev_write_iter,
> - .mmap = generic_file_mmap,
> + .mmap = blkdev_mmap,
> .fsync = blkdev_fsync,
> .unlocked_ioctl = block_ioctl,
> #ifdef CONFIG_COMPAT
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 72d8a844c692..8fb2d4b848bf 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -482,6 +482,9 @@ struct block_device {
> int bd_fsfreeze_count;
> /* Mutex for freeze */
> struct mutex bd_fsfreeze_mutex;
> +#ifdef CONFIG_FS_DAX
> + int bd_map_count;
> +#endif
> };
>
> /*
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 9b964a5920af..cc2f0fdae707 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -152,6 +152,8 @@ struct inodes_stat_t {
> #define BLKSECDISCARD _IO(0x12,125)
> #define BLKROTATIONAL _IO(0x12,126)
> #define BLKZEROOUT _IO(0x12,127)
> +#define BLKDAXSET _IO(0x12,128)
> +#define BLKDAXGET _IO(0x12,129)
>
> #define BMAP_IOCTL 1 /* obsolete - kept for compatibility */
> #define FIBMAP _IO(0x00,1) /* bmap access */
>
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