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Date: Fri, 11 Mar 2022 09:23:18 -0500
From: Jeff Layton <jlayton@...nel.org>
To: David Howells <dhowells@...hat.com>, linux-cachefs@...hat.com
Cc: ceph-devel@...r.kernel.org, linux-afs@...ts.infradead.org,
Jeffle Xu <jefflexu@...ux.alibaba.com>,
Anna Schumaker <anna.schumaker@...app.com>,
Steve French <sfrench@...ba.org>,
Dominique Martinet <asmadeus@...ewreck.org>,
David Wysochanski <dwysocha@...hat.com>,
Ilya Dryomov <idryomov@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
v9fs-developer@...ts.sourceforge.net,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/20] netfs: Prep for write helpers
On Thu, 2022-03-10 at 16:13 +0000, David Howells wrote:
> Having had a go at implementing write helpers and content encryption
> support in netfslib, it seems that the netfs_read_{,sub}request structs and
> the equivalent write request structs were almost the same and so should be
> merged, thereby requiring only one set of alloc/get/put functions and a
> common set of tracepoints.
>
> Merging the structs also has the advantage that if a bounce buffer is added
> to the request struct, a read operation can be performed to fill the bounce
> buffer, the contents of the buffer can be modified and then a write
> operation can be performed on it to send the data wherever it needs to go
> using the same request structure all the way through. The I/O handlers
> would then transparently perform any required crypto. This should make it
> easy to perform RMW cycles if needed.
>
> The potentially common functions and structs, however, by their names all
> proclaim themselves to be associated with the read side of things. The
> bulk of these changes alter this in the following ways:
>
> (1) Rename struct netfs_read_{,sub}request to netfs_io_{,sub}request.
>
> (2) Rename some enums, members and flags to make them more appropriate.
>
> (3) Adjust some comments to match.
>
> (4) Drop "read"/"rreq" from the names of common functions. For instance,
> netfs_get_read_request() becomes netfs_get_request().
>
> (5) The ->init_rreq() and ->issue_op() methods become ->init_request() and
> ->issue_read(). I've kept the latter as a read-specific function and
> in another branch added an ->issue_write() method.
>
> The driver source is then reorganised into a number of files:
>
> fs/netfs/buffered_read.c Create read reqs to the pagecache
> fs/netfs/io.c Dispatchers for read and write reqs
> fs/netfs/main.c Some general miscellaneous bits
> fs/netfs/objects.c Alloc, get and put functions
> fs/netfs/stats.c Optional procfs statistics.
>
> and future development can be fitted into this scheme, e.g.:
>
> fs/netfs/buffered_write.c Modify the pagecache
> fs/netfs/buffered_flush.c Writeback from the pagecache
> fs/netfs/direct_read.c DIO read support
> fs/netfs/direct_write.c DIO write support
> fs/netfs/unbuffered_write.c Write modifications directly back
>
> Beyond the above changes, there are also some changes that affect how
> things work:
>
> (1) Make fscache_end_operation() generally available.
>
> (2) In the netfs tracing header, generate enums from the symbol -> string
> mapping tables rather than manually coding them.
>
> (3) Add a struct for filesystems that uses netfslib to put into their
> inode wrapper structs to hold extra state that netfslib is interested
> in, such as the fscache cookie. This allows netfslib functions to be
> set in filesystem operation tables and jumped to directly without
> having to have a filesystem wrapper.
>
> (4) Add a member to the struct added in (3) to track the remote inode
> length as that may differ if local modifications are buffered. We may
> need to supply an appropriate EOF pointer when storing data (in AFS
> for example).
>
> (5) Pass extra information to netfs_alloc_request() so that the
> ->init_request() hook can access it and retain information to indicate
> the origin of the operation.
>
> (6) Make the ->init_request() hook return an error, thereby allowing a
> filesystem that isn't allowed to cache an inode (ceph or cifs, for
> example) to skip readahead.
>
> (7) Switch to using refcount_t for subrequests and add tracepoints to log
> refcount changes for the request and subrequest structs.
>
> (8) Add a function to consolidate dispatching a read request. Similar
> code is used in three places and another couple are likely to be added
> in the future.
>
>
> The patches can be found on this branch:
>
> http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-next
>
> This is based on top of ceph's master branch as some of the patches
> conflict.
>
> David
> ---
>
> Changes
> =======
> ver #3)
> - Rebased one patch back on the ceph tree as the top patch got removed[4].
> - Split out the bit to move ceph cap-getting on readahead out from the
> patch adding an inode context[5].
> - Made ceph_init_request() store the caps got in rreq->netfs_priv for
> later freeing.
> - Comment the need to keep the netfs inode context contiguous with the VFS
> inode struct[6].
> - Altered the traces to use 'R=' consistently to denote a request debug ID.
>
> ver #2)
> - Changed kdoc references to renamed files[1].
> - Switched the begin-read-function patch and the prepare-to-split patch as
> fewer functions then need unstatic'ing.
> - Fixed an uninitialised var in netfs_begin_read()[2][3].
> - Fixed a refleak caused by an unremoved line when netfs_begin_read() was
> introduced.
> - Used "#if IS_ENABLED()" in netfs_i_cookie(), not "#ifdef".
> - Implemented missing bit of ceph readahead through netfs_readahead().
> - Rearranged the patch order to make the ceph readahead possible.
>
> Link: https://lore.kernel.org/r/20220303202811.6a1d53a1@canb.auug.org.au/ [1]
> Link: https://lore.kernel.org/r/20220303163826.1120936-1-nathan@kernel.org/ [2]
> Link: https://lore.kernel.org/r/20220303235647.1297171-1-colin.i.king@gmail.com/ [3]
> Link: https://lore.kernel.org/r/527234d849b0de18b326d6db0d59070b70d19b7e.camel@kernel.org/ [4]
> Link: https://lore.kernel.org/r/8af0d47f17d89c06bbf602496dd845f2b0bf25b3.camel@kernel.org/ [5]
> Link: https://lore.kernel.org/r/beaf4f6a6c2575ed489adb14b257253c868f9a5c.camel@kernel.org/ [6]
> Link: https://lore.kernel.org/r/164622970143.3564931.3656393397237724303.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/164678185692.1200972.597611902374126174.stgit@warthog.procyon.org.uk/ # v2
>
> ---
> David Howells (19):
> netfs: Generate enums from trace symbol mapping lists
> netfs: Rename netfs_read_*request to netfs_io_*request
> netfs: Finish off rename of netfs_read_request to netfs_io_request
> netfs: Split netfs_io_* object handling out
> netfs: Adjust the netfs_rreq tracepoint slightly
> netfs: Trace refcounting on the netfs_io_request struct
> netfs: Trace refcounting on the netfs_io_subrequest struct
> netfs: Adjust the netfs_failure tracepoint to indicate non-subreq lines
> netfs: Refactor arguments for netfs_alloc_read_request
> netfs: Change ->init_request() to return an error code
> ceph: Make ceph_init_request() check caps on readahead
> netfs: Add a netfs inode context
> netfs: Add a function to consolidate beginning a read
> netfs: Prepare to split read_helper.c
> netfs: Rename read_helper.c to io.c
> netfs: Split fs/netfs/read_helper.c
> netfs: Split some core bits out into their own file
> netfs: Keep track of the actual remote file size
> afs: Maintain netfs_i_context::remote_i_size
>
> Jeffle Xu (1):
> fscache: export fscache_end_operation()
>
>
> Documentation/filesystems/netfs_library.rst | 140 ++-
> fs/9p/cache.c | 10 +-
> fs/9p/v9fs.c | 4 +-
> fs/9p/v9fs.h | 13 +-
> fs/9p/vfs_addr.c | 62 +-
> fs/9p/vfs_inode.c | 13 +-
> fs/afs/dynroot.c | 1 +
> fs/afs/file.c | 41 +-
> fs/afs/inode.c | 32 +-
> fs/afs/internal.h | 23 +-
> fs/afs/super.c | 4 +-
> fs/afs/write.c | 10 +-
> fs/cachefiles/io.c | 10 +-
> fs/ceph/addr.c | 116 +-
> fs/ceph/cache.c | 28 +-
> fs/ceph/cache.h | 15 +-
> fs/ceph/inode.c | 6 +-
> fs/ceph/super.h | 17 +-
> fs/cifs/cifsglob.h | 10 +-
> fs/cifs/fscache.c | 19 +-
> fs/cifs/fscache.h | 2 +-
> fs/fscache/internal.h | 11 -
> fs/netfs/Makefile | 8 +-
> fs/netfs/buffered_read.c | 428 +++++++
> fs/netfs/internal.h | 49 +-
> fs/netfs/io.c | 657 ++++++++++
> fs/netfs/main.c | 20 +
> fs/netfs/objects.c | 160 +++
> fs/netfs/read_helper.c | 1205 -------------------
> fs/netfs/stats.c | 1 -
> fs/nfs/fscache.c | 8 -
> include/linux/fscache.h | 14 +
> include/linux/netfs.h | 162 ++-
> include/trace/events/cachefiles.h | 6 +-
> include/trace/events/netfs.h | 190 ++-
> 35 files changed, 1867 insertions(+), 1628 deletions(-)
> create mode 100644 fs/netfs/buffered_read.c
> create mode 100644 fs/netfs/io.c
> create mode 100644 fs/netfs/main.c
> create mode 100644 fs/netfs/objects.c
> delete mode 100644 fs/netfs/read_helper.c
>
>
I ran this through xfstests on ceph, with fscache enabled and it seemed
to do fine.
Tested-by: Jeff Layton <jlayton@...nel.org>
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