On 11/29/21 10:28 PM, David Howells wrote:
> Pass more information to the cache on how to deal with a hole if it
> encounters one when trying to read from the cache. Three options are
> provided:
>
> (1) NETFS_READ_HOLE_IGNORE. Read the hole along with the data, assuming
> it to be a punched-out extent by the backing filesystem.
>
> (2) NETFS_READ_HOLE_CLEAR. If there's a hole, erase the requested region
> of the cache and clear the read buffer.
>
> (3) NETFS_READ_HOLE_FAIL. Fail the read if a hole is detected.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: linux-cachefs@xxxxxxxxxx
> ---
>
> fs/netfs/read_helper.c | 8 ++++----
> include/linux/netfs.h | 11 ++++++++++-
> 2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
> index 7dc79fa8a1f3..08df413efdf3 100644
> --- a/fs/netfs/read_helper.c
> +++ b/fs/netfs/read_helper.c
> @@ -170,7 +170,7 @@ static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error
> */
> static void netfs_read_from_cache(struct netfs_read_request *rreq,
> struct netfs_read_subrequest *subreq,
> - bool seek_data)
> + enum netfs_read_from_hole read_hole)
> {
> struct netfs_cache_resources *cres = &rreq->cache_resources;
> struct iov_iter iter;
> @@ -180,7 +180,7 @@ static void netfs_read_from_cache(struct netfs_read_request *rreq,
> subreq->start + subreq->transferred,
> subreq->len - subreq->transferred);
>
> - cres->ops->read(cres, subreq->start, &iter, seek_data,
> + cres->ops->read(cres, subreq->start, &iter, read_hole,
> netfs_cache_read_terminated, subreq);
> }
>
> @@ -466,7 +466,7 @@ static void netfs_rreq_short_read(struct netfs_read_request *rreq,
> netfs_get_read_subrequest(subreq);
> atomic_inc(&rreq->nr_rd_ops);
> if (subreq->source == NETFS_READ_FROM_CACHE)
> - netfs_read_from_cache(rreq, subreq, true);
> + netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_CLEAR);
Hi I'm not sure why NETFS_READ_HOLE_CLEAR style should be used in 'short
read' case.
Besides,
```
static void netfs_read_from_cache(struct netfs_read_request *rreq,
struct netfs_read_subrequest *subreq,
enum netfs_read_from_hole read_hole)
{
struct netfs_cache_resources *cres = &rreq->cache_resources;
struct iov_iter iter;
netfs_stat(&netfs_n_rh_read);
iov_iter_xarray(&iter, READ, &rreq->mapping->i_pages,
subreq->start + subreq->transferred,
subreq->len - subreq->transferred);
cres->ops->read(cres, subreq->start, &iter, read_hole,
netfs_cache_read_terminated, subreq);
}
```
I'm not sure why 'subreq->start' is not incremented with
'subreq->transferred' when calling cres->ops->read() in 'short read' case.
> else
> netfs_read_from_server(rreq, subreq);
> }
> @@ -794,7 +794,7 @@ static bool netfs_rreq_submit_slice(struct netfs_read_request *rreq,
> netfs_read_from_server(rreq, subreq);
> break;
> case NETFS_READ_FROM_CACHE:
> - netfs_read_from_cache(rreq, subreq, false);
> + netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_IGNORE);
> break;
> default:
> BUG();
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index 5a46fde65759..b46c39d98bbd 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -196,6 +196,15 @@ struct netfs_read_request_ops {
> void (*cleanup)(struct address_space *mapping, void *netfs_priv);
> };
>
> +/*
> + * How to handle reading from a hole.
> + */
> +enum netfs_read_from_hole {
> + NETFS_READ_HOLE_IGNORE,
> + NETFS_READ_HOLE_CLEAR,
> + NETFS_READ_HOLE_FAIL,
> +};
> +
> /*
> * Table of operations for access to a cache. This is obtained by
> * rreq->ops->begin_cache_operation().
> @@ -208,7 +217,7 @@ struct netfs_cache_ops {
> int (*read)(struct netfs_cache_resources *cres,
> loff_t start_pos,
> struct iov_iter *iter,
> - bool seek_data,
> + enum netfs_read_from_hole read_hole,
> netfs_io_terminated_t term_func,
> void *term_func_priv);
>
>
--
Thanks,
Jeffle
