Re: [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[John Groves]

On 24/02/26 12:56PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:54 -0600
> John Groves <John@xxxxxxxxxx> wrote:
> 
> > Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
> > the function that opens a block (pmem) device and the struct
> > dax_holder_operations that are needed for that ABI.
> > 
> > In this commit, support for opening character /dev/dax is stubbed. A
> > later commit introduces this capability.
> > 
> > Signed-off-by: John Groves <john@xxxxxxxxxx>
> 
> Formatting comments mostly same as previous patches, so I'll stop repeating them.

I tried to bulk apply those recommendations.

> 
> > ---
> >  fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 83 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 3329aff000d1..82c861998093 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
> >  	.show_options	= famfs_show_options,
> >  };
> >  
> > +/***************************************************************************************
> > + * dax_holder_operations for block dax
> > + */
> > +
> > +static int
> > +famfs_blk_dax_notify_failure(
> > +	struct dax_device	*dax_devp,
> > +	u64			offset,
> > +	u64			len,
> > +	int			mf_flags)
> > +{
> > +
> > +	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
> > +	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> > +	.notify_failure		= famfs_blk_dax_notify_failure,
> > +};
> > +
> > +static int
> > +famfs_open_char_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> > +	       __func__, fc->source);
> > +	return -ENODEV;
> > +}
> > +
> > +/**
> > + * famfs_open_device()
> > + *
> > + * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
> > + * Otherwise try to open it as a block/pmem device.
> > + */
> > +static int
> > +famfs_open_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	struct famfs_fs_info *fsi = sb->s_fs_info;
> > +	struct dax_device    *dax_devp;
> > +	u64 start_off = 0;
> > +	struct bdev_handle   *handlep;
> Definitely don't force alignment in local parameter definitions.
> Always goes wrong and makes for unreadable mess in patches!

Okay, undone. Everywhere.

> 
> > +
> > +	if (fsi->dax_devp) {
> > +		pr_err("%s: already mounted\n", __func__);
> Fine to fail but worth a error message? Not sure on convention on this but seems noisy
> and maybe in userspace control which isn't good.

Changing to pr_debug. Would be good to have access to it in that way

> > +		return -EALREADY;
> > +	}
> > +
> > +	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
> > +		return famfs_open_char_device(sb, fc);
> > +
> > +	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
> > +		pr_err("%s: primary backing dev (%s) is not pmem\n",
> > +		       __func__, fc->source);
> > +		return -EINVAL;
> > +	}
> > +
> > +	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
> > +	if (IS_ERR(handlep->bdev)) {
> > +		pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
> > +		return PTR_ERR(handlep->bdev);
> > +	}
> > +
> > +	dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
> > +				      fsi  /* holder */,
> > +				      &famfs_blk_dax_holder_ops);
> > +	if (IS_ERR(dax_devp)) {
> > +		pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
> > +		bdev_release(handlep);
> > +		return -ENODEV;
> > +	}
> > +	fsi->bdev_handle = handlep;
> > +	fsi->dax_devp    = dax_devp;
> > +
> > +	pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);
> 
> pr_debug()  Kernel log is too noisy anyway! + I'd assume we can tell this succeeded
> in lots of other ways.

Done

> 
> 
> > +	return 0;
> > +}
> > +
> > +
> >  
> >  MODULE_LICENSE("GPL");

Thanks,
John
>