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Message-ID: <c0d893bf6f52702a0bd2056a8cb005861b8324ea.camel@kernel.org>
Date: Fri, 04 Nov 2022 07:18:07 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>, dhowells@...hat.com,
xiang@...nel.org, chao@...nel.org, linux-cachefs@...hat.com,
linux-erofs@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] fscache,cachefiles: add prepare_ondemand_read()
callback
On Fri, 2022-11-04 at 15:26 +0800, Jingbo Xu wrote:
> Add prepare_ondemand_read() callback dedicated for the on-demand read
> scenario, so that callers from this scenario can be decoupled from
> netfs_io_subrequest.
>
> To reuse the hole detecting logic as mush as possible, both the
> implementation of prepare_read() and prepare_ondemand_read() inside
> Cachefiles call a common routine.
>
> In the near future, prepare_read() will get enhanced and more
> information will be needed and then returned to callers. Thus
> netfs_io_subrequest is a reasonable candidate for holding places for all
> these information needed in the internal implementation.
>
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> ---
> fs/cachefiles/io.c | 42 +++++++++++++++++++++++++------
> include/linux/netfs.h | 7 ++++++
> include/trace/events/cachefiles.h | 4 +--
> 3 files changed, 43 insertions(+), 10 deletions(-)
>
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index 000a28f46e59..6427259fcba9 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -385,16 +385,11 @@ static int cachefiles_write(struct netfs_cache_resources *cres,
> term_func, term_func_priv);
> }
>
> -/*
> - * Prepare a read operation, shortening it to a cached/uncached
> - * boundary as appropriate.
> - */
> -static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *subreq,
> - loff_t i_size)
> +static enum netfs_io_source cachefiles_do_prepare_read(struct netfs_io_subrequest *subreq,
> + struct netfs_cache_resources *cres,
> + loff_t i_size)
> {
> enum cachefiles_prepare_read_trace why;
> - struct netfs_io_request *rreq = subreq->rreq;
> - struct netfs_cache_resources *cres = &rreq->cache_resources;
> struct cachefiles_object *object;
> struct cachefiles_cache *cache;
> struct fscache_cookie *cookie = fscache_cres_cookie(cres);
> @@ -501,6 +496,36 @@ static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *
> return ret;
> }
>
> +/*
> + * Prepare a read operation, shortening it to a cached/uncached
> + * boundary as appropriate.
> + */
> +static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *subreq,
> + loff_t i_size)
> +{
> + return cachefiles_do_prepare_read(subreq,
> + &subreq->rreq->cache_resources, i_size);
> +}
> +
> +/*
> + * Prepare an on-demand read operation, shortening it to a cached/uncached
> + * boundary as appropriate.
> + */
> +static enum netfs_io_source cachefiles_prepare_ondemand_read(struct netfs_cache_resources *cres,
> + loff_t start, size_t *_len, loff_t i_size)
> +{
> + enum netfs_io_source source;
> + struct netfs_io_subrequest subreq = {
> + .start = start,
> + .len = *_len,
> + .flags = 1 << NETFS_SREQ_ONDEMAND,
> + };
> +
Faking up a struct like this is sort of fragile. What if we change
cachefiles_do_prepare_read to consult other fields in this structure
later?
It might be best to have cachefiles_do_prepare_read take individual
start, len, and flags values instead of doing this.
> + source = cachefiles_do_prepare_read(&subreq, cres, i_size);
> + *_len = subreq.len;
> + return source;
> +}
> +
> /*
> * Prepare for a write to occur.
> */
> @@ -621,6 +646,7 @@ static const struct netfs_cache_ops cachefiles_netfs_cache_ops = {
> .write = cachefiles_write,
> .prepare_read = cachefiles_prepare_read,
> .prepare_write = cachefiles_prepare_write,
> + .prepare_ondemand_read = cachefiles_prepare_ondemand_read,
> .query_occupancy = cachefiles_query_occupancy,
> };
>
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index f2402ddeafbf..d82071c37133 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -267,6 +267,13 @@ struct netfs_cache_ops {
> loff_t *_start, size_t *_len, loff_t i_size,
> bool no_space_allocated_yet);
>
> + /* Prepare an on-demand read operation, shortening it to a cached/uncached
> + * boundary as appropriate.
> + */
> + enum netfs_io_source (*prepare_ondemand_read)(struct netfs_cache_resources *cres,
> + loff_t start, size_t *_len,
> + loff_t i_size);
> +
> /* Query the occupancy of the cache in a region, returning where the
> * next chunk of data starts and how long it is.
> */
> diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
> index d8d4d73fe7b6..655d5900b8ef 100644
> --- a/include/trace/events/cachefiles.h
> +++ b/include/trace/events/cachefiles.h
> @@ -448,14 +448,14 @@ TRACE_EVENT(cachefiles_prep_read,
> ),
>
> TP_fast_assign(
> - __entry->rreq = sreq->rreq->debug_id;
> + __entry->rreq = sreq->rreq ? sreq->rreq->debug_id : 0;
> __entry->index = sreq->debug_index;
> __entry->flags = sreq->flags;
> __entry->source = source;
> __entry->why = why;
> __entry->len = sreq->len;
> __entry->start = sreq->start;
> - __entry->netfs_inode = sreq->rreq->inode->i_ino;
> + __entry->netfs_inode = sreq->rreq ? sreq->rreq->inode->i_ino : 0;
> __entry->cache_inode = cache_inode;
> ),
>
--
Jeff Layton <jlayton@...nel.org>
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