Re: [RFC PATCH 32/35] netfs: Add some more RMW support for ceph

From: Viacheslav Dubeyko
Date: Wed Mar 19 2025 - 15:16:59 EST

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On Thu, 2025-03-13 at 23:33 +0000, David Howells wrote:
> Add some support for RMW in ceph:
>
> (1) Add netfs_unbuffered_read_from_inode() to allow reading from an inode
> without having a file pointer so that truncate can modify a
> now-partial tail block of a content-encrypted file.
>
> This takes an additional argument to cause it to fail or give a short
> read if a hole is encountered. This is noted on the request with
> NETFS_RREQ_NO_READ_HOLE for the filesystem to pick up.
>
> (2) Set NETFS_RREQ_RMW when doing an RMW as part of a request.
>
> (3) Provide a ->rmw_read_done() op for netfslib to tell the filesystem
> that it has completed the read required for RMW.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: Viacheslav Dubeyko <slava@xxxxxxxxxxx>
> cc: Alex Markuze <amarkuze@xxxxxxxxxx>
> cc: Ilya Dryomov <idryomov@xxxxxxxxx>
> cc: ceph-devel@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> ---
> fs/netfs/direct_read.c | 75 ++++++++++++++++++++++++++++++++++++
> fs/netfs/direct_write.c | 1 +
> fs/netfs/main.c | 1 +
> fs/netfs/objects.c | 1 +
> fs/netfs/read_collect.c | 2 +
> fs/netfs/write_retry.c | 3 ++
> include/linux/netfs.h | 7 ++++
> include/trace/events/netfs.h | 3 ++
> 8 files changed, 93 insertions(+)
>
> diff --git a/fs/netfs/direct_read.c b/fs/netfs/direct_read.c
> index 5e4bd1e5a378..4061f934dfe6 100644
> --- a/fs/netfs/direct_read.c
> +++ b/fs/netfs/direct_read.c
> @@ -373,3 +373,78 @@ ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter)
> return ret;
> }
> EXPORT_SYMBOL(netfs_unbuffered_read_iter);
> +
> +/**
> + * netfs_unbuffered_read_from_inode - Perform an unbuffered sync I/O read
> + * @inode: The inode being accessed
> + * @pos: The file position to read from
> + * @iter: The output buffer (also specifies read length)
> + * @nohole: True to return short/ENODATA if hole encountered
> + *
> + * Perform a synchronous unbuffered I/O from the inode to the output buffer.
> + * No use is made of the pagecache. The output buffer must be suitably aligned
> + * if content encryption is to be used. If @nohole is true then the read will
> + * stop short if a hole is encountered and return -ENODATA if the read begins
> + * with a hole.
> + *
> + * The caller must hold any appropriate locks.
> + */
> +ssize_t netfs_unbuffered_read_from_inode(struct inode *inode, loff_t pos,
> + struct iov_iter *iter, bool nohole)
> +{
> + struct netfs_io_request *rreq;
> + ssize_t ret;
> + size_t orig_count = iov_iter_count(iter);
> +
> + _enter("");
> +
> + if (WARN_ON(user_backed_iter(iter)))
> + return -EIO;
> +
> + if (!orig_count)
> + return 0; /* Don't update atime */
> +
> + ret = filemap_write_and_wait_range(inode->i_mapping, pos, orig_count);
> + if (ret < 0)
> + return ret;
> + inode_update_time(inode, S_ATIME);
> +
> + rreq = netfs_alloc_request(inode->i_mapping, NULL, pos, orig_count,
> + NULL, NETFS_UNBUFFERED_READ);
> + if (IS_ERR(rreq))
> + return PTR_ERR(rreq);
> +
> + ret = -EIO;
> + if (test_bit(NETFS_RREQ_CONTENT_ENCRYPTION, &rreq->flags) &&
> + WARN_ON(!netfs_is_crypto_aligned(rreq, iter)))
> + goto out;
> +
> + netfs_stat(&netfs_n_rh_dio_read);
> + trace_netfs_read(rreq, rreq->start, rreq->len,
> + netfs_read_trace_unbuffered_read_from_inode);
> +
> + rreq->buffer.iter = *iter;

The struct iov_iter structure is complex enough and we assign it by value to
rreq->buffer.iter. So, the initial pointer will not receive any changes then. Is
it desired behavior here?

Thanks,
Slava.

> + rreq->len = orig_count;
> + rreq->direct_bv_unpin = false;
> + iov_iter_advance(iter, orig_count);
> +
> + if (nohole)
> + __set_bit(NETFS_RREQ_NO_READ_HOLE, &rreq->flags);
> +
> + /* We're going to do the crypto in place in the destination buffer. */
> + if (test_bit(NETFS_RREQ_CONTENT_ENCRYPTION, &rreq->flags))
> + __set_bit(NETFS_RREQ_CRYPT_IN_PLACE, &rreq->flags);
> +
> + ret = netfs_dispatch_unbuffered_reads(rreq);
> +
> + if (!rreq->submitted) {
> + netfs_put_request(rreq, false, netfs_rreq_trace_put_no_submit);
> + goto out;
> + }
> +
> + ret = netfs_wait_for_read(rreq);
> +out:
> + netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
> + return ret;
> +}
> +EXPORT_SYMBOL(netfs_unbuffered_read_from_inode);
> diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
> index 83c5c06c4710..a99722f90c71 100644
> --- a/fs/netfs/direct_write.c
> +++ b/fs/netfs/direct_write.c
> @@ -145,6 +145,7 @@ static ssize_t netfs_write_through_bounce_buffer(struct netfs_io_request *wreq,
> wreq->start = gstart;
> wreq->len = gend - gstart;
>
> + __set_bit(NETFS_RREQ_RMW, &ictx->flags);
> if (gstart >= end) {
> /* At or after EOF, nothing to read. */
> } else {
> diff --git a/fs/netfs/main.c b/fs/netfs/main.c
> index 07f8cffbda8c..0900dea53e4a 100644
> --- a/fs/netfs/main.c
> +++ b/fs/netfs/main.c
> @@ -39,6 +39,7 @@ static const char *netfs_origins[nr__netfs_io_origin] = {
> [NETFS_READ_GAPS] = "RG",
> [NETFS_READ_SINGLE] = "R1",
> [NETFS_READ_FOR_WRITE] = "RW",
> + [NETFS_UNBUFFERED_READ] = "UR",
> [NETFS_DIO_READ] = "DR",
> [NETFS_WRITEBACK] = "WB",
> [NETFS_WRITEBACK_SINGLE] = "W1",
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index 4606e830c116..958c4d460d07 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -60,6 +60,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
> origin == NETFS_READ_GAPS ||
> origin == NETFS_READ_SINGLE ||
> origin == NETFS_READ_FOR_WRITE ||
> + origin == NETFS_UNBUFFERED_READ ||
> origin == NETFS_DIO_READ) {
> INIT_WORK(&rreq->work, netfs_read_collection_worker);
> rreq->io_streams[0].avail = true;
> diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
> index 0a0bff90ca9e..013a90738dcd 100644
> --- a/fs/netfs/read_collect.c
> +++ b/fs/netfs/read_collect.c
> @@ -462,6 +462,7 @@ static void netfs_read_collection(struct netfs_io_request *rreq)
> //netfs_rreq_is_still_valid(rreq);
>
> switch (rreq->origin) {
> + case NETFS_UNBUFFERED_READ:
> case NETFS_DIO_READ:
> case NETFS_READ_GAPS:
> case NETFS_RMW_READ:
> @@ -681,6 +682,7 @@ ssize_t netfs_wait_for_read(struct netfs_io_request *rreq)
> if (ret == 0) {
> ret = rreq->transferred;
> switch (rreq->origin) {
> + case NETFS_UNBUFFERED_READ:
> case NETFS_DIO_READ:
> case NETFS_READ_SINGLE:
> ret = rreq->transferred;
> diff --git a/fs/netfs/write_retry.c b/fs/netfs/write_retry.c
> index f727b48e2bfe..9e4e79d5a403 100644
> --- a/fs/netfs/write_retry.c
> +++ b/fs/netfs/write_retry.c
> @@ -386,6 +386,9 @@ ssize_t netfs_rmw_read(struct netfs_io_request *wreq, struct file *file,
> ret = 0;
> }
>
> + if (ret == 0 && rreq->netfs_ops->rmw_read_done)
> + rreq->netfs_ops->rmw_read_done(wreq, rreq);
> +
> error:
> netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
> return ret;
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index 9d17d4bd9753..4049c985b9b4 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -220,6 +220,7 @@ enum netfs_io_origin {
> NETFS_READ_GAPS, /* This read is a synchronous read to fill gaps */
> NETFS_READ_SINGLE, /* This read should be treated as a single object */
> NETFS_READ_FOR_WRITE, /* This read is to prepare a write */
> + NETFS_UNBUFFERED_READ, /* This is an unbuffered I/O read */
> NETFS_DIO_READ, /* This is a direct I/O read */
> NETFS_WRITEBACK, /* This write was triggered by writepages */
> NETFS_WRITEBACK_SINGLE, /* This monolithic write was triggered by writepages */
> @@ -308,6 +309,9 @@ struct netfs_io_request {
> #define NETFS_RREQ_CONTENT_ENCRYPTION 16 /* Content encryption is in use */
> #define NETFS_RREQ_CRYPT_IN_PLACE 17 /* Do decryption in place */
> #define NETFS_RREQ_PUT_RMW_TAIL 18 /* Need to put ->rmw_tail */
> +#define NETFS_RREQ_RMW 19 /* Performing RMW cycle */
> +#define NETFS_RREQ_REPEAT_RMW 20 /* Need to perform an RMW cycle */
> +#define NETFS_RREQ_NO_READ_HOLE 21 /* Give short read/error if hole encountered */
> #define NETFS_RREQ_USE_PGPRIV2 31 /* [DEPRECATED] Use PG_private_2 to mark
> * write to cache on read */
> const struct netfs_request_ops *netfs_ops;
> @@ -336,6 +340,7 @@ struct netfs_request_ops {
> /* Modification handling */
> void (*update_i_size)(struct inode *inode, loff_t i_size);
> void (*post_modify)(struct inode *inode, void *fs_priv);
> + void (*rmw_read_done)(struct netfs_io_request *wreq, struct netfs_io_request *rreq);
>
> /* Write request handling */
> void (*begin_writeback)(struct netfs_io_request *wreq);
> @@ -432,6 +437,8 @@ ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *i
> ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
> ssize_t netfs_buffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
> ssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter);
> +ssize_t netfs_unbuffered_read_from_inode(struct inode *inode, loff_t pos,
> + struct iov_iter *iter, bool nohole);
>
> /* High-level write API */
> ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
> diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
> index 74af82d773bd..9254c6f0e604 100644
> --- a/include/trace/events/netfs.h
> +++ b/include/trace/events/netfs.h
> @@ -23,6 +23,7 @@
> EM(netfs_read_trace_read_gaps, "READ-GAPS") \
> EM(netfs_read_trace_read_single, "READ-SNGL") \
> EM(netfs_read_trace_prefetch_for_write, "PREFETCHW") \
> + EM(netfs_read_trace_unbuffered_read_from_inode, "READ-INOD") \
> E_(netfs_read_trace_write_begin, "WRITEBEGN")
>
> #define netfs_write_traces \
> @@ -38,6 +39,7 @@
> EM(NETFS_READ_GAPS, "RG") \
> EM(NETFS_READ_SINGLE, "R1") \
> EM(NETFS_READ_FOR_WRITE, "RW") \
> + EM(NETFS_UNBUFFERED_READ, "UR") \
> EM(NETFS_DIO_READ, "DR") \
> EM(NETFS_WRITEBACK, "WB") \
> EM(NETFS_WRITEBACK_SINGLE, "W1") \
> @@ -104,6 +106,7 @@
> EM(netfs_sreq_trace_io_progress, "IO ") \
> EM(netfs_sreq_trace_limited, "LIMIT") \
> EM(netfs_sreq_trace_need_clear, "N-CLR") \
> + EM(netfs_sreq_trace_need_rmw, "N-RMW") \
> EM(netfs_sreq_trace_partial_read, "PARTR") \
> EM(netfs_sreq_trace_need_retry, "ND-RT") \
> EM(netfs_sreq_trace_pending, "PEND ") \
>
>

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