On 06/21/2018 02:28 PM, Matthew Wilcox wrote:
> The new API is much easier for this user. Also add kerneldoc for
> get_anon_bdev().
>
> Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> ---
> fs/super.c | 63 +++++++++++++++++++-----------------------------------
> 1 file changed, 22 insertions(+), 41 deletions(-)
>
> diff --git a/fs/super.c b/fs/super.c
> index 50728d9c1a05..3e7a0aea716a 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -978,58 +978,42 @@ void emergency_thaw_all(void)
> }
> }
>
> -/*
> - * Unnamed block devices are dummy devices used by virtual
> - * filesystems which don't use real block-devices. -- jrs
> - */
> -
> static DEFINE_IDA(unnamed_dev_ida);
> -static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
> -/* Many userspace utilities consider an FSID of 0 invalid.
> - * Always return at least 1 from get_anon_bdev.
> - */
> -static int unnamed_dev_start = 1;
>
> +/**
> + * get_anon_bdev - Allocate a block device for filesystems which don't have one.
> + * @p: Pointer to a dev_t.
> + *
> + * Filesystems which don't use real block devices can call this function
> + * to allocate a virtual block device.
> + *
> + * Context: Any context. Frequently called while holding sb_lock.
> + * Return: 0 on success, -EMFILE if there are no anonymous bdevs left
> + * or -EAGAIN if memory allocation failed.
Looks to me like the code used to return -ENOMEM and used -EAGAIN as an
internal retry code.
confused? (/me)
> + */
> int get_anon_bdev(dev_t *p)
> {
> int dev;
> - int error;
>
> - retry:
> - if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
> - return -ENOMEM;
> - spin_lock(&unnamed_dev_lock);
> - error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
> - if (!error)
> - unnamed_dev_start = dev + 1;
> - spin_unlock(&unnamed_dev_lock);
> - if (error == -EAGAIN)
> - /* We raced and lost with another CPU. */
> - goto retry;
> - else if (error)
> + /*
> + * Many userspace utilities consider an FSID of 0 invalid.
> + * Always return at least 1 from get_anon_bdev.
> + */
> + dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1,
> + GFP_ATOMIC);
> + if (dev == -ENOSPC)
> + return -EMFILE;
> + if (dev < 0)
> return -EAGAIN;
>
> - if (dev >= (1 << MINORBITS)) {
> - spin_lock(&unnamed_dev_lock);
> - ida_remove(&unnamed_dev_ida, dev);
> - if (unnamed_dev_start > dev)
> - unnamed_dev_start = dev;
> - spin_unlock(&unnamed_dev_lock);
> - return -EMFILE;
> - }
> - *p = MKDEV(0, dev & MINORMASK);
> + *p = MKDEV(0, dev);
> return 0;
> }
> EXPORT_SYMBOL(get_anon_bdev);
--
~Randy
