Re: [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch

Jonathan Cameron
2024-02-26T13:52:33Z

On Fri, 23 Feb 2024 11:42:02 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the ability to open a character /dev/dax device
> instead of a block /dev/pmem device. This rests on the dev_dax_iomap
> patches earlier in this series.

Not sure the back reference is needed given it's in the series.

>
> Signed-off-by: John Groves <john@groves.net>
> ---
> fs/famfs/famfs_inode.c | 97 +++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 87 insertions(+), 10 deletions(-)
>
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 0d659820e8ff..7d65ac497147 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -215,6 +215,93 @@ static const struct super_operations famfs_ops = {
> .show_options = famfs_show_options,
> };
>
> +/*****************************************************************************/
> +
> +#if defined(CONFIG_DEV_DAX_IOMAP)
> +
> +/*
> + * famfs dax_operations (for char dax)
> + */
> +static int
> +famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
> + u64 len, int mf_flags)
> +{
> + pr_err("%s: offset %lld len %llu flags %x\n", __func__,
> + offset, len, mf_flags);
> + return -EOPNOTSUPP;
> +}
> +
> +static const struct dax_holder_operations famfs_dax_holder_ops = {
> + .notify_failure = famfs_dax_notify_failure,
> +};
> +
> +/*****************************************************************************/
> +
> +/**
> + * famfs_open_char_device()
> + *
> + * Open a /dev/dax device. This only works in kernels with the dev_dax_iomap patch

That comment you definitely don't need as this won't get merged without
that patch being in place.

> + */
> +static int
> +famfs_open_char_device(
> + struct super_block *sb,
> + struct fs_context *fc)
> +{
> + struct famfs_fs_info *fsi = sb->s_fs_info;
> + struct dax_device *dax_devp;
> + struct inode *daxdev_inode;
> +
> + int rc = 0;
set in all paths where it's used.

> +
> + pr_notice("%s: Opening character dax device %s\n", __func__, fc->source);

pr_debug

> +
> + fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
> + if (IS_ERR(fsi->dax_filp)) {
> + pr_err("%s: failed to open dax device %s\n",
> + __func__, fc->source);
> + fsi->dax_filp = NULL;
Better to use a local variable

fp = filp_open(fc->source, O_RDWR, 0);
if (IS_ERR(fp)) {
pr_err.
return;
}
fsi->dax_filp = fp;
or similar.

> + return PTR_ERR(fsi->dax_filp);
> + }
> +
> + daxdev_inode = file_inode(fsi->dax_filp);
> + dax_devp = inode_dax(daxdev_inode);
> + if (IS_ERR(dax_devp)) {
> + pr_err("%s: unable to get daxdev from inode for %s\n",
> + __func__, fc->source);
> + rc = -ENODEV;
> + goto char_err;
> + }
> +
> + rc = fs_dax_get(dax_devp, fsi, &famfs_dax_holder_ops);
> + if (rc) {
> + pr_info("%s: err attaching famfs_dax_holder_ops\n", __func__);
> + goto char_err;
> + }
> +
> + fsi->bdev_handle = NULL;
> + fsi->dax_devp = dax_devp;
> +
> + return 0;
> +
> +char_err:
> + filp_close(fsi->dax_filp, NULL);

You carefully set fsi->dax_filp to null in other other error paths.
Why there and not here?

> + return rc;
> +}
> +
> +#else /* CONFIG_DEV_DAX_IOMAP */
> +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;
> +}
> +
> +
> +#endif /* CONFIG_DEV_DAX_IOMAP */
> +
> /***************************************************************************************
> * dax_holder_operations for block dax
> */
> @@ -236,16 +323,6 @@ const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> .notify_failure = famfs_blk_dax_notify_failure,
> };
>

Put it in right place earlier! Makes this less noisy.

> -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()
> *