9p: Add fscache support to 9p

This patch adds a persistent, read-only caching facility for
9p clients using the FS-Cache caching backend.

When the fscache facility is enabled, each inode is associated
with a corresponding vcookie which is an index into the FS-Cache
indexing tree. The FS-Cache indexing tree is indexed at 3 levels:
- session object associated with each mount.
- inode/vcookie
- actual data (pages)

A cache tag is chosen randomly for each session. These tags can
be read off /sys/fs/9p/caches and can be passed as a mount-time
parameter to re-attach to the specified caching session.

Signed-off-by: Abhishek Kulkarni <adkulkar@umail.iu.edu>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 474 insertions, 0 deletions

diff --git a/fs/9p/cache.c b/fs/9p/cache.c
new file mode 100644
index 000000000000..51c94e26a346
--- /dev/null
+++ b/fs/9p/cache.c
@@ -0,0 +1,474 @@
+/*
+ * V9FS cache definitions.
+ *
+ *  Copyright (C) 2009 by Abhishek Kulkarni <adkulkar@umail.iu.edu>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2
+ *  as published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to:
+ *  Free Software Foundation
+ *  51 Franklin Street, Fifth Floor
+ *  Boston, MA  02111-1301  USA
+ *
+ */
+
+#include <linux/jiffies.h>
+#include <linux/file.h>
+#include <linux/stat.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <net/9p/9p.h>
+
+#include "v9fs.h"
+#include "cache.h"
+
+#define CACHETAG_LEN  11
+
+struct kmem_cache *vcookie_cache;
+
+struct fscache_netfs v9fs_cache_netfs = {
+        .name           = "9p",
+        .version        = 0,
+};
+
+static void init_once(void *foo)
+{
+        struct v9fs_cookie *vcookie = (struct v9fs_cookie *) foo;
+        vcookie->fscache = NULL;
+        vcookie->qid = NULL;
+        inode_init_once(&vcookie->inode);
+}
+
+/**
+ * v9fs_init_vcookiecache - initialize a cache for vcookies to maintain
+ *                          vcookie to inode mapping
+ *
+ * Returns 0 on success.
+ */
+
+static int v9fs_init_vcookiecache(void)
+{
+        vcookie_cache = kmem_cache_create("vcookie_cache",
+                                          sizeof(struct v9fs_cookie),
+                                          0, (SLAB_RECLAIM_ACCOUNT|
+                                              SLAB_MEM_SPREAD),
+                                          init_once);
+        if (!vcookie_cache)
+                return -ENOMEM;
+
+        return 0;
+}
+
+/**
+ * v9fs_destroy_vcookiecache - destroy the cache of vcookies
+ *
+ */
+
+static void v9fs_destroy_vcookiecache(void)
+{
+        kmem_cache_destroy(vcookie_cache);
+}
+
+int __v9fs_cache_register(void)
+{
+        int ret;
+        ret = v9fs_init_vcookiecache();
+        if (ret < 0)
+                return ret;
+
+        return fscache_register_netfs(&v9fs_cache_netfs);
+}
+
+void __v9fs_cache_unregister(void)
+{
+        v9fs_destroy_vcookiecache();
+        fscache_unregister_netfs(&v9fs_cache_netfs);
+}
+
+/**
+ * v9fs_random_cachetag - Generate a random tag to be associated
+ *                        with a new cache session.
+ *
+ * The value of jiffies is used for a fairly randomly cache tag.
+ */
+
+static
+int v9fs_random_cachetag(struct v9fs_session_info *v9ses)
+{
+        v9ses->cachetag = kmalloc(CACHETAG_LEN, GFP_KERNEL);
+        if (!v9ses->cachetag)
+                return -ENOMEM;
+
+        return scnprintf(v9ses->cachetag, CACHETAG_LEN, "%lu", jiffies);
+}
+
+static uint16_t v9fs_cache_session_get_key(const void *cookie_netfs_data,
+                                           void *buffer, uint16_t bufmax)
+{
+        struct v9fs_session_info *v9ses;
+        uint16_t klen = 0;
+
+        v9ses = (struct v9fs_session_info *)cookie_netfs_data;
+        P9_DPRINTK(P9_DEBUG_FSC, "session %p buf %p size %u", v9ses,
+                   buffer, bufmax);
+
+        if (v9ses->cachetag)
+                klen = strlen(v9ses->cachetag);
+
+        if (klen > bufmax)
+                return 0;
+
+        memcpy(buffer, v9ses->cachetag, klen);
+        P9_DPRINTK(P9_DEBUG_FSC, "cache session tag %s", v9ses->cachetag);
+        return klen;
+}
+
+const struct fscache_cookie_def v9fs_cache_session_index_def = {
+        .name           = "9P.session",
+        .type           = FSCACHE_COOKIE_TYPE_INDEX,
+        .get_key        = v9fs_cache_session_get_key,
+};
+
+void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
+{
+        /* If no cache session tag was specified, we generate a random one. */
+        if (!v9ses->cachetag)
+                v9fs_random_cachetag(v9ses);
+
+        v9ses->fscache = fscache_acquire_cookie(v9fs_cache_netfs.primary_index,
+                                                &v9fs_cache_session_index_def,
+                                                v9ses);
+        P9_DPRINTK(P9_DEBUG_FSC, "session %p get cookie %p", v9ses,
+                   v9ses->fscache);
+}
+
+void v9fs_cache_session_put_cookie(struct v9fs_session_info *v9ses)
+{
+        P9_DPRINTK(P9_DEBUG_FSC, "session %p put cookie %p", v9ses,
+                   v9ses->fscache);
+        fscache_relinquish_cookie(v9ses->fscache, 0);
+        v9ses->fscache = NULL;
+}
+
+
+static uint16_t v9fs_cache_inode_get_key(const void *cookie_netfs_data,
+                                         void *buffer, uint16_t bufmax)
+{
+        const struct v9fs_cookie *vcookie = cookie_netfs_data;
+        memcpy(buffer, &vcookie->qid->path, sizeof(vcookie->qid->path));
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p get key %llu", &vcookie->inode,
+                   vcookie->qid->path);
+        return sizeof(vcookie->qid->path);
+}
+
+static void v9fs_cache_inode_get_attr(const void *cookie_netfs_data,
+                                      uint64_t *size)
+{
+        const struct v9fs_cookie *vcookie = cookie_netfs_data;
+        *size = i_size_read(&vcookie->inode);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p get attr %llu", &vcookie->inode,
+                   *size);
+}
+
+static uint16_t v9fs_cache_inode_get_aux(const void *cookie_netfs_data,
+                                         void *buffer, uint16_t buflen)
+{
+        const struct v9fs_cookie *vcookie = cookie_netfs_data;
+        memcpy(buffer, &vcookie->qid->version, sizeof(vcookie->qid->version));
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p get aux %u", &vcookie->inode,
+                   vcookie->qid->version);
+        return sizeof(vcookie->qid->version);
+}
+
+static enum
+fscache_checkaux v9fs_cache_inode_check_aux(void *cookie_netfs_data,
+                                            const void *buffer,
+                                            uint16_t buflen)
+{
+        const struct v9fs_cookie *vcookie = cookie_netfs_data;
+
+        if (buflen != sizeof(vcookie->qid->version))
+                return FSCACHE_CHECKAUX_OBSOLETE;
+
+        if (memcmp(buffer, &vcookie->qid->version,
+                   sizeof(vcookie->qid->version)))
+                return FSCACHE_CHECKAUX_OBSOLETE;
+
+        return FSCACHE_CHECKAUX_OKAY;
+}
+
+static void v9fs_cache_inode_now_uncached(void *cookie_netfs_data)
+{
+        struct v9fs_cookie *vcookie = cookie_netfs_data;
+        struct pagevec pvec;
+        pgoff_t first;
+        int loop, nr_pages;
+
+        pagevec_init(&pvec, 0);
+        first = 0;
+
+        for (;;) {
+                nr_pages = pagevec_lookup(&pvec, vcookie->inode.i_mapping,
+                                          first,
+                                          PAGEVEC_SIZE - pagevec_count(&pvec));
+                if (!nr_pages)
+                        break;
+
+                for (loop = 0; loop < nr_pages; loop++)
+                        ClearPageFsCache(pvec.pages[loop]);
+
+                first = pvec.pages[nr_pages - 1]->index + 1;
+
+                pvec.nr = nr_pages;
+                pagevec_release(&pvec);
+                cond_resched();
+        }
+}
+
+const struct fscache_cookie_def v9fs_cache_inode_index_def = {
+        .name           = "9p.inode",
+        .type           = FSCACHE_COOKIE_TYPE_DATAFILE,
+        .get_key        = v9fs_cache_inode_get_key,
+        .get_attr       = v9fs_cache_inode_get_attr,
+        .get_aux        = v9fs_cache_inode_get_aux,
+        .check_aux      = v9fs_cache_inode_check_aux,
+        .now_uncached   = v9fs_cache_inode_now_uncached,
+};
+
+void v9fs_cache_inode_get_cookie(struct inode *inode)
+{
+        struct v9fs_cookie *vcookie;
+        struct v9fs_session_info *v9ses;
+
+        if (!S_ISREG(inode->i_mode))
+                return;
+
+        vcookie = v9fs_inode2cookie(inode);
+        if (vcookie->fscache)
+                return;
+
+        v9ses = v9fs_inode2v9ses(inode);
+        vcookie->fscache = fscache_acquire_cookie(v9ses->fscache,
+                                                  &v9fs_cache_inode_index_def,
+                                                  vcookie);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p get cookie %p", inode,
+                   vcookie->fscache);
+}
+
+void v9fs_cache_inode_put_cookie(struct inode *inode)
+{
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        if (!vcookie->fscache)
+                return;
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p put cookie %p", inode,
+                   vcookie->fscache);
+
+        fscache_relinquish_cookie(vcookie->fscache, 0);
+        vcookie->fscache = NULL;
+}
+
+void v9fs_cache_inode_flush_cookie(struct inode *inode)
+{
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        if (!vcookie->fscache)
+                return;
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p flush cookie %p", inode,
+                   vcookie->fscache);
+
+        fscache_relinquish_cookie(vcookie->fscache, 1);
+        vcookie->fscache = NULL;
+}
+
+void v9fs_cache_inode_set_cookie(struct inode *inode, struct file *filp)
+{
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+        struct p9_fid *fid;
+
+        if (!vcookie->fscache)
+                return;
+
+        spin_lock(&vcookie->lock);
+        fid = filp->private_data;
+        if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
+                v9fs_cache_inode_flush_cookie(inode);
+        else
+                v9fs_cache_inode_get_cookie(inode);
+
+        spin_unlock(&vcookie->lock);
+}
+
+void v9fs_cache_inode_reset_cookie(struct inode *inode)
+{
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+        struct v9fs_session_info *v9ses;
+        struct fscache_cookie *old;
+
+        if (!vcookie->fscache)
+                return;
+
+        old = vcookie->fscache;
+
+        spin_lock(&vcookie->lock);
+        fscache_relinquish_cookie(vcookie->fscache, 1);
+
+        v9ses = v9fs_inode2v9ses(inode);
+        vcookie->fscache = fscache_acquire_cookie(v9ses->fscache,
+                                                  &v9fs_cache_inode_index_def,
+                                                  vcookie);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p revalidating cookie old %p new %p",
+                   inode, old, vcookie->fscache);
+
+        spin_unlock(&vcookie->lock);
+}
+
+int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
+{
+        struct inode *inode = page->mapping->host;
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        BUG_ON(!vcookie->fscache);
+
+        if (PageFsCache(page)) {
+                if (fscache_check_page_write(vcookie->fscache, page)) {
+                        if (!(gfp & __GFP_WAIT))
+                                return 0;
+                        fscache_wait_on_page_write(vcookie->fscache, page);
+                }
+
+                fscache_uncache_page(vcookie->fscache, page);
+                ClearPageFsCache(page);
+        }
+
+        return 1;
+}
+
+void __v9fs_fscache_invalidate_page(struct page *page)
+{
+        struct inode *inode = page->mapping->host;
+        struct v9fs_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        BUG_ON(!vcookie->fscache);
+
+        if (PageFsCache(page)) {
+                fscache_wait_on_page_write(vcookie->fscache, page);
+                BUG_ON(!PageLocked(page));
+                fscache_uncache_page(vcookie->fscache, page);
+                ClearPageFsCache(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_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p page %p", inode, page);
+        if (!vcookie->fscache)
+                return -ENOBUFS;
+
+        ret = fscache_read_or_alloc_page(vcookie->fscache,
+                                         page,
+                                         v9fs_vfs_readpage_complete,
+                                         NULL,
+                                         GFP_KERNEL);
+        switch (ret) {
+        case -ENOBUFS:
+        case -ENODATA:
+                P9_DPRINTK(P9_DEBUG_FSC, "page/inode not in cache %d", ret);
+                return 1;
+        case 0:
+                P9_DPRINTK(P9_DEBUG_FSC, "BIO submitted");
+                return ret;
+        default:
+                P9_DPRINTK(P9_DEBUG_FSC, "ret %d", 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_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p pages %u", inode, *nr_pages);
+        if (!vcookie->fscache)
+                return -ENOBUFS;
+
+        ret = fscache_read_or_alloc_pages(vcookie->fscache,
+                                          mapping, pages, nr_pages,
+                                          v9fs_vfs_readpage_complete,
+                                          NULL,
+                                          mapping_gfp_mask(mapping));
+        switch (ret) {
+        case -ENOBUFS:
+        case -ENODATA:
+                P9_DPRINTK(P9_DEBUG_FSC, "pages/inodes not in cache %d", ret);
+                return 1;
+        case 0:
+                BUG_ON(!list_empty(pages));
+                BUG_ON(*nr_pages != 0);
+                P9_DPRINTK(P9_DEBUG_FSC, "BIO submitted");
+                return ret;
+        default:
+                P9_DPRINTK(P9_DEBUG_FSC, "ret %d", 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_cookie *vcookie = v9fs_inode2cookie(inode);
+
+        P9_DPRINTK(P9_DEBUG_FSC, "inode %p page %p", inode, page);
+        ret = fscache_write_page(vcookie->fscache, page, GFP_KERNEL);
+        P9_DPRINTK(P9_DEBUG_FSC, "ret =  %d", ret);
+        if (ret != 0)
+                v9fs_uncache_page(inode, page);
+}