Messages in this thread | | | Subject | Re: [PATCH] loop: properly observe rotational flag of underlying device | From | Jens Axboe <> | Date | Wed, 11 Nov 2015 14:29:37 -0700 |
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On 11/11/2015 08:21 AM, Holger Hoffstätte wrote: > > The loop driver always declares the rotational flag of its device as > rotational, even when the device of the mapped file is nonrotational, > as is the case with SSDs or on tmpfs. This can confuse filesystem tools > which are SSD-aware; in my case I frequently forget to tell mkfs.btrfs > that my loop device on tmpfs is nonrotational, and that I really don't > need any automatic metadata redundancy. > > The attached patch fixes this by introspecting the rotational flag of the > mapped file's underlying block device, if it exists. If the mapped file's > filesystem has no associated block device - as is the case on e.g. tmpfs - > we assume nonrotational storage. If there is a better way to identify such > non-devices I'd love to hear them. > > Signed-off-by: Holger Hoffstätte <holger.hoffstaette@googlemail.com> > --- > drivers/block/loop.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 423f4ca..2984aca 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -843,6 +843,24 @@ static void loop_config_discard(struct loop_device *lo) > queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q); > } > > +static void loop_update_rotational(struct loop_device *lo) > +{ > + struct file *file = lo->lo_backing_file; > + struct inode *file_inode = file->f_mapping->host; > + struct block_device *file_bdev = file_inode->i_sb->s_bdev; > + struct request_queue *q = lo->lo_queue; > + bool nonrot = true; > + > + /* not all filesystems (e.g. tmpfs) have a sb->s_bdev */ > + if (file_bdev) > + nonrot = blk_queue_nonrot(bdev_get_queue(file_bdev)); > + > + if (nonrot) > + queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q); > + else > + queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q); > +}
Are we sure we want to change the default from rot to nonrot?
Apart from that, looks good.
-- Jens Axboe
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