[PATCH v2 4/8] 9p: (untested) Convert to using the netfs helper lib to do reads and caching

From: David Howells
Date: Fri Sep 17 2021 - 11:05:35 EST

Convert the 9p filesystem to use the netfs helper lib to handle readpage,
readahead and write_begin, converting those into a common issue_op for the
filesystem itself to handle. The netfs helper lib also handles reading
from fscache if a cache is available, and interleaving reads from both
sources.

This change also switches from the old fscache I/O API to the new one,
meaning that fscache no longer keeps track of netfs pages and instead does
async DIO between the backing files and the 9p file pagecache. As a part
of this change, the handling of PG_fscache changes. It now just means that
the cache has a write I/O operation in progress on a page (PG_locked
is used for a read I/O op).

Note that this is a cut-down version of the fscache rewrite and does not
change any of the cookie and cache coherency handling.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
cc: v9fs-developer@xxxxxxxxxxxxxxxxxxxxx
cc: linux-cachefs@xxxxxxxxxx
Link: https://lore.kernel.org/r/163162772646.438332.16323773205855053535.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
---

fs/9p/Kconfig | 1
fs/9p/cache.c | 137 -------------------------------------------
fs/9p/cache.h | 99 +------------------------------
fs/9p/v9fs.h | 9 +++
fs/9p/vfs_addr.c | 174 ++++++++++++++++++++++++------------------------------
fs/9p/vfs_file.c | 21 +++++--
6 files changed, 108 insertions(+), 333 deletions(-)

diff --git a/fs/9p/Kconfig b/fs/9p/Kconfig
index 09fd4a185fd2..d7bc93447c85 100644
--- a/fs/9p/Kconfig
+++ b/fs/9p/Kconfig
@@ -2,6 +2,7 @@
config 9P_FS
tristate "Plan 9 Resource Sharing Support (9P2000)"
depends on INET && NET_9P
+ select NETFS_SUPPORT
help
If you say Y here, you will get experimental support for
Plan 9 resource sharing via the 9P2000 protocol.
diff --git a/fs/9p/cache.c b/fs/9p/cache.c
index eb2151fb6049..68e5d12e690d 100644
--- a/fs/9p/cache.c
+++ b/fs/9p/cache.c
@@ -199,140 +199,3 @@ void v9fs_cache_inode_reset_cookie(struct inode *inode)

mutex_unlock(&v9inode->fscache_lock);
}
-
-int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
-{
- struct inode *inode = page->mapping->host;
- struct v9fs_inode *v9inode = V9FS_I(inode);
-
- BUG_ON(!v9inode->fscache);
-
- return fscache_maybe_release_page(v9inode->fscache, page, gfp);
-}
-
-void __v9fs_fscache_invalidate_page(struct page *page)
-{
- struct inode *inode = page->mapping->host;
- struct v9fs_inode *v9inode = V9FS_I(inode);
-
- BUG_ON(!v9inode->fscache);
-
- if (PageFsCache(page)) {
- fscache_wait_on_page_write(v9inode->fscache, page);
- BUG_ON(!PageLocked(page));
- fscache_uncache_page(v9inode->fscache, page);
- }
-}
-
-static void v9fs_vfs_readpage_complete(struct page *page, void *data,
- int error)
-{
- if (!error)
- SetPageUptodate(page);
-
- unlock_page(page);
-}
-
-/**
- * __v9fs_readpage_from_fscache - read a page from cache
- *
- * Returns 0 if the pages are in cache and a BIO is submitted,
- * 1 if the pages are not in cache and -error otherwise.
- */
-
-int __v9fs_readpage_from_fscache(struct inode *inode, struct page *page)
-{
- int ret;
- const struct v9fs_inode *v9inode = V9FS_I(inode);
-
- p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
- if (!v9inode->fscache)
- return -ENOBUFS;
-
- ret = fscache_read_or_alloc_page(v9inode->fscache,
- page,
- v9fs_vfs_readpage_complete,
- NULL,
- GFP_KERNEL);
- switch (ret) {
- case -ENOBUFS:
- case -ENODATA:
- p9_debug(P9_DEBUG_FSC, "page/inode not in cache %d\n", ret);
- return 1;
- case 0:
- p9_debug(P9_DEBUG_FSC, "BIO submitted\n");
- return ret;
- default:
- p9_debug(P9_DEBUG_FSC, "ret %d\n", ret);
- return ret;
- }
-}
-
-/**
- * __v9fs_readpages_from_fscache - read multiple pages from cache
- *
- * Returns 0 if the pages are in cache and a BIO is submitted,
- * 1 if the pages are not in cache and -error otherwise.
- */
-
-int __v9fs_readpages_from_fscache(struct inode *inode,
- struct address_space *mapping,
- struct list_head *pages,
- unsigned *nr_pages)
-{
- int ret;
- const struct v9fs_inode *v9inode = V9FS_I(inode);
-
- p9_debug(P9_DEBUG_FSC, "inode %p pages %u\n", inode, *nr_pages);
- if (!v9inode->fscache)
- return -ENOBUFS;
-
- ret = fscache_read_or_alloc_pages(v9inode->fscache,
- mapping, pages, nr_pages,
- v9fs_vfs_readpage_complete,
- NULL,
- mapping_gfp_mask(mapping));
- switch (ret) {
- case -ENOBUFS:
- case -ENODATA:
- p9_debug(P9_DEBUG_FSC, "pages/inodes not in cache %d\n", ret);
- return 1;
- case 0:
- BUG_ON(!list_empty(pages));
- BUG_ON(*nr_pages != 0);
- p9_debug(P9_DEBUG_FSC, "BIO submitted\n");
- return ret;
- default:
- p9_debug(P9_DEBUG_FSC, "ret %d\n", ret);
- return ret;
- }
-}
-
-/**
- * __v9fs_readpage_to_fscache - write a page to the cache
- *
- */
-
-void __v9fs_readpage_to_fscache(struct inode *inode, struct page *page)
-{
- int ret;
- const struct v9fs_inode *v9inode = V9FS_I(inode);
-
- p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
- ret = fscache_write_page(v9inode->fscache, page,
- i_size_read(&v9inode->vfs_inode), GFP_KERNEL);
- p9_debug(P9_DEBUG_FSC, "ret = %d\n", ret);
- if (ret != 0)
- v9fs_uncache_page(inode, page);
-}
-
-/*
- * wait for a page to complete writing to the cache
- */
-void __v9fs_fscache_wait_on_page_write(struct inode *inode, struct page *page)
-{
- const struct v9fs_inode *v9inode = V9FS_I(inode);
- p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
- if (PageFsCache(page))
- fscache_wait_on_page_write(v9inode->fscache, page);
-}
diff --git a/fs/9p/cache.h b/fs/9p/cache.h
index c7e74776ce90..cfafa89b972c 100644
--- a/fs/9p/cache.h
+++ b/fs/9p/cache.h
@@ -7,10 +7,11 @@

#ifndef _9P_CACHE_H
#define _9P_CACHE_H
-#ifdef CONFIG_9P_FSCACHE
-#define FSCACHE_USE_OLD_IO_API
+
+#define FSCACHE_USE_NEW_IO_API
#include <linux/fscache.h>
-#include <linux/spinlock.h>
+
+#ifdef CONFIG_9P_FSCACHE

extern struct fscache_netfs v9fs_cache_netfs;
extern const struct fscache_cookie_def v9fs_cache_session_index_def;
@@ -28,64 +29,6 @@ extern void v9fs_cache_inode_reset_cookie(struct inode *inode);
extern int __v9fs_cache_register(void);
extern void __v9fs_cache_unregister(void);

-extern int __v9fs_fscache_release_page(struct page *page, gfp_t gfp);
-extern void __v9fs_fscache_invalidate_page(struct page *page);
-extern int __v9fs_readpage_from_fscache(struct inode *inode,
- struct page *page);
-extern int __v9fs_readpages_from_fscache(struct inode *inode,
- struct address_space *mapping,
- struct list_head *pages,
- unsigned *nr_pages);
-extern void __v9fs_readpage_to_fscache(struct inode *inode, struct page *page);
-extern void __v9fs_fscache_wait_on_page_write(struct inode *inode,
- struct page *page);
-
-static inline int v9fs_fscache_release_page(struct page *page,
- gfp_t gfp)
-{
- return __v9fs_fscache_release_page(page, gfp);
-}
-
-static inline void v9fs_fscache_invalidate_page(struct page *page)
-{
- __v9fs_fscache_invalidate_page(page);
-}
-
-static inline int v9fs_readpage_from_fscache(struct inode *inode,
- struct page *page)
-{
- return __v9fs_readpage_from_fscache(inode, page);
-}
-
-static inline int v9fs_readpages_from_fscache(struct inode *inode,
- struct address_space *mapping,
- struct list_head *pages,
- unsigned *nr_pages)
-{
- return __v9fs_readpages_from_fscache(inode, mapping, pages,
- nr_pages);
-}
-
-static inline void v9fs_readpage_to_fscache(struct inode *inode,
- struct page *page)
-{
- if (PageFsCache(page))
- __v9fs_readpage_to_fscache(inode, page);
-}
-
-static inline void v9fs_uncache_page(struct inode *inode, struct page *page)
-{
- struct v9fs_inode *v9inode = V9FS_I(inode);
- fscache_uncache_page(v9inode->fscache, page);
- BUG_ON(PageFsCache(page));
-}
-
-static inline void v9fs_fscache_wait_on_page_write(struct inode *inode,
- struct page *page)
-{
- return __v9fs_fscache_wait_on_page_write(inode, page);
-}
-
#else /* CONFIG_9P_FSCACHE */

static inline void v9fs_cache_inode_get_cookie(struct inode *inode)
@@ -100,39 +43,5 @@ static inline void v9fs_cache_inode_set_cookie(struct inode *inode, struct file
{
}

-static inline int v9fs_fscache_release_page(struct page *page,
- gfp_t gfp) {
- return 1;
-}
-
-static inline void v9fs_fscache_invalidate_page(struct page *page) {}
-
-static inline int v9fs_readpage_from_fscache(struct inode *inode,
- struct page *page)
-{
- return -ENOBUFS;
-}
-
-static inline int v9fs_readpages_from_fscache(struct inode *inode,
- struct address_space *mapping,
- struct list_head *pages,
- unsigned *nr_pages)
-{
- return -ENOBUFS;
-}
-
-static inline void v9fs_readpage_to_fscache(struct inode *inode,
- struct page *page)
-{}
-
-static inline void v9fs_uncache_page(struct inode *inode, struct page *page)
-{}
-
-static inline void v9fs_fscache_wait_on_page_write(struct inode *inode,
- struct page *page)
-{
- return;
-}
-
#endif /* CONFIG_9P_FSCACHE */
#endif /* _9P_CACHE_H */
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index 4ca56c5dd637..07332f135b38 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -123,6 +123,15 @@ static inline struct v9fs_inode *V9FS_I(const struct inode *inode)
{
return container_of(inode, struct v9fs_inode, vfs_inode);
}
+
+static inline struct fscache_cookie *v9fs_inode_cookie(struct v9fs_inode *v9inode)
+{
+#ifdef CONFIG_9P_FSCACHE
+ return v9inode->fscache;
+#else
+ return NULL;
+#endif
+}

extern int v9fs_show_options(struct seq_file *m, struct dentry *root);

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index cce9ace651a2..a7e080916826 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -19,7 +19,7 @@
#include <linux/idr.h>
#include <linux/sched.h>
#include <linux/uio.h>
-#include <linux/bvec.h>
+#include <linux/netfs.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>

@@ -29,89 +29,82 @@
#include "fid.h"

/**
- * v9fs_fid_readpage - read an entire page in from 9P
- *
- * @fid: fid being read
- * @page: structure to page
- *
+ * v9fs_req_issue_op - Issue a read from 9P
+ * @subreq: The read to make
*/
-static int v9fs_fid_readpage(void *data, struct page *page)
+static void v9fs_req_issue_op(struct netfs_read_subrequest *subreq)
{
- struct p9_fid *fid = data;
- struct inode *inode = page->mapping->host;
- struct bio_vec bvec = {.bv_page = page, .bv_len = PAGE_SIZE};
+ struct netfs_read_request *rreq = subreq->rreq;
+ struct p9_fid *fid = rreq->netfs_priv;
struct iov_iter to;
+ loff_t pos = subreq->start + subreq->transferred;
+ size_t len = subreq->len - subreq->transferred;
int retval, err;

- p9_debug(P9_DEBUG_VFS, "\n");
-
- BUG_ON(!PageLocked(page));
+ iov_iter_xarray(&to, READ, &rreq->mapping->i_pages, pos, len);

- retval = v9fs_readpage_from_fscache(inode, page);
- if (retval == 0)
- return retval;
+ retval = p9_client_read(fid, pos, &to, &err);
+ if (retval)
+ subreq->error = retval;
+}

- iov_iter_bvec(&to, READ, &bvec, 1, PAGE_SIZE);
+/**
+ * v9fs_init_rreq - Initialise a read request
+ * @rreq: The read request
+ * @file: The file being read from
+ */
+static void v9fs_init_rreq(struct netfs_read_request *rreq, struct file *file)
+{
+ rreq->netfs_priv = file->private_data;
+}

- retval = p9_client_read(fid, page_offset(page), &to, &err);
- if (err) {
- v9fs_uncache_page(inode, page);
- retval = err;
- goto done;
- }
+/**
+ * v9fs_is_cache_enabled - Determine if caching is enabled for an inode
+ * @inode: The inode to check
+ */
+static bool v9fs_is_cache_enabled(struct inode *inode)
+{
+ struct fscache_cookie *cookie = v9fs_inode_cookie(V9FS_I(inode));

- zero_user(page, retval, PAGE_SIZE - retval);
- flush_dcache_page(page);
- SetPageUptodate(page);
+ return fscache_cookie_enabled(cookie) && !hlist_empty(&cookie->backing_objects);
+}

- v9fs_readpage_to_fscache(inode, page);
- retval = 0;
+/**
+ * v9fs_begin_cache_operation - Begin a cache operation for a read
+ * @rreq: The read request
+ */
+static int v9fs_begin_cache_operation(struct netfs_read_request *rreq)
+{
+ struct fscache_cookie *cookie = v9fs_inode_cookie(V9FS_I(rreq->inode));

-done:
- unlock_page(page);
- return retval;
+ return fscache_begin_read_operation(&rreq->cache_resources, cookie);
}

+static const struct netfs_read_request_ops v9fs_req_ops = {
+ .init_rreq = v9fs_init_rreq,
+ .is_cache_enabled = v9fs_is_cache_enabled,
+ .begin_cache_operation = v9fs_begin_cache_operation,
+ .issue_op = v9fs_req_issue_op,
+};
+
/**
* v9fs_vfs_readpage - read an entire page in from 9P
- *
* @filp: file being read
* @page: structure to page
*
*/
-
-static int v9fs_vfs_readpage(struct file *filp, struct page *page)
+static int v9fs_vfs_readpage(struct file *file, struct page *page)
{
- return v9fs_fid_readpage(filp->private_data, page);
+ return netfs_readpage(file, page, &v9fs_req_ops, NULL);
}

/**
- * v9fs_vfs_readpages - read a set of pages from 9P
- *
- * @filp: file being read
- * @mapping: the address space
- * @pages: list of pages to read
- * @nr_pages: count of pages to read
- *
+ * v9fs_vfs_readahead - read a set of pages from 9P
+ * @ractl: The readahead parameters
*/
-
-static int v9fs_vfs_readpages(struct file *filp, struct address_space *mapping,
- struct list_head *pages, unsigned nr_pages)
+static void v9fs_vfs_readahead(struct readahead_control *ractl)
{
- int ret = 0;
- struct inode *inode;
-
- inode = mapping->host;
- p9_debug(P9_DEBUG_VFS, "inode: %p file: %p\n", inode, filp);
-
- ret = v9fs_readpages_from_fscache(inode, mapping, pages, &nr_pages);
- if (ret == 0)
- return ret;
-
- ret = read_cache_pages(mapping, pages, v9fs_fid_readpage,
- filp->private_data);
- p9_debug(P9_DEBUG_VFS, " = %d\n", ret);
- return ret;
+ netfs_readahead(ractl, &v9fs_req_ops, NULL);
}

/**
@@ -124,7 +117,14 @@ static int v9fs_release_page(struct page *page, gfp_t gfp)
{
if (PagePrivate(page))
return 0;
- return v9fs_fscache_release_page(page, gfp);
+#ifdef CONFIG_AFS_FSCACHE
+ if (PageFsCache(page)) {
+ if (!(gfp & __GFP_DIRECT_RECLAIM) || !(gfp & __GFP_FS))
+ return 0;
+ wait_on_page_fscache(page);
+ }
+#endif
+ return 1;
}

/**
@@ -137,21 +137,16 @@ static int v9fs_release_page(struct page *page, gfp_t gfp)
static void v9fs_invalidate_page(struct page *page, unsigned int offset,
unsigned int length)
{
- /*
- * If called with zero offset, we should release
- * the private state assocated with the page
- */
- if (offset == 0 && length == PAGE_SIZE)
- v9fs_fscache_invalidate_page(page);
+ wait_on_page_fscache(page);
}

static int v9fs_vfs_writepage_locked(struct page *page)
{
struct inode *inode = page->mapping->host;
struct v9fs_inode *v9inode = V9FS_I(inode);
+ loff_t start = page_offset(page);
loff_t size = i_size_read(inode);
struct iov_iter from;
- struct bio_vec bvec;
int err, len;

if (page->index == size >> PAGE_SHIFT)
@@ -159,17 +154,14 @@ static int v9fs_vfs_writepage_locked(struct page *page)
else
len = PAGE_SIZE;

- bvec.bv_page = page;
- bvec.bv_offset = 0;
- bvec.bv_len = len;
- iov_iter_bvec(&from, WRITE, &bvec, 1, len);
+ iov_iter_xarray(&from, WRITE, &page->mapping->i_pages, start, len);

/* We should have writeback_fid always set */
BUG_ON(!v9inode->writeback_fid);

set_page_writeback(page);

- p9_client_write(v9inode->writeback_fid, page_offset(page), &from, &err);
+ p9_client_write(v9inode->writeback_fid, start, &from, &err);

end_page_writeback(page);
return err;
@@ -205,14 +197,13 @@ static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
static int v9fs_launder_page(struct page *page)
{
int retval;
- struct inode *inode = page->mapping->host;

- v9fs_fscache_wait_on_page_write(inode, page);
if (clear_page_dirty_for_io(page)) {
retval = v9fs_vfs_writepage_locked(page);
if (retval)
return retval;
}
+ wait_on_page_fscache(page);
return 0;
}

@@ -256,35 +247,24 @@ static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
{
- int retval = 0;
+ int retval;
struct page *page;
- struct v9fs_inode *v9inode;
- pgoff_t index = pos >> PAGE_SHIFT;
- struct inode *inode = mapping->host;
-
+ struct v9fs_inode *v9inode = V9FS_I(mapping->host);

p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);

- v9inode = V9FS_I(inode);
-start:
- page = grab_cache_page_write_begin(mapping, index, flags);
- if (!page) {
- retval = -ENOMEM;
- goto out;
- }
BUG_ON(!v9inode->writeback_fid);
- if (PageUptodate(page))
- goto out;

- if (len == PAGE_SIZE)
- goto out;
+ /* Prefetch area to be written into the cache if we're caching this
+ * file. We need to do this before we get a lock on the page in case
+ * there's more than one writer competing for the same cache block.
+ */
+ retval = netfs_write_begin(filp, mapping, pos, len, flags, &page, fsdata,
+ &v9fs_req_ops, NULL);
+ if (retval < 0)
+ return retval;

- retval = v9fs_fid_readpage(v9inode->writeback_fid, page);
- put_page(page);
- if (!retval)
- goto start;
-out:
- *pagep = page;
+ *pagep = find_subpage(page, pos / PAGE_SIZE);
return retval;
}

@@ -324,7 +304,7 @@ static int v9fs_write_end(struct file *filp, struct address_space *mapping,

const struct address_space_operations v9fs_addr_operations = {
.readpage = v9fs_vfs_readpage,
- .readpages = v9fs_vfs_readpages,
+ .readahead = v9fs_vfs_readahead,
.set_page_dirty = __set_page_dirty_nobuffers,
.writepage = v9fs_vfs_writepage,
.write_begin = v9fs_write_begin,
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index aab5e6538660..4b617d10cf28 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -542,14 +542,27 @@ v9fs_vm_page_mkwrite(struct vm_fault *vmf)
p9_debug(P9_DEBUG_VFS, "page %p fid %lx\n",
page, (unsigned long)filp->private_data);

+ v9inode = V9FS_I(inode);
+
+ /* Wait for the page to be written to the cache before we allow it to
+ * be modified. We then assume the entire page will need writing back.
+ */
+#ifdef CONFIG_V9FS_FSCACHE
+ if (PageFsCache(page) &&
+ wait_on_page_bit_killable(page, PG_fscache) < 0)
+ return VM_FAULT_RETRY;
+#endif
+
+ if (PageWriteback(page) &&
+ wait_on_page_bit_killable(page, PG_writeback) < 0)
+ return VM_FAULT_RETRY;
+
/* Update file times before taking page lock */
file_update_time(filp);

- v9inode = V9FS_I(inode);
- /* make sure the cache has finished storing the page */
- v9fs_fscache_wait_on_page_write(inode, page);
BUG_ON(!v9inode->writeback_fid);
- lock_page(page);
+ if (lock_page_killable(page) < 0)
+ return VM_FAULT_RETRY;
if (page->mapping != inode->i_mapping)
goto out_unlock;
wait_for_stable_page(page);