[RFC PATCH 43/61] fscache: Implement "will_modify" parameter on fscache_use_cookie()

From: David Howells
Date: Mon May 04 2020 - 13:14:28 EST

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Implement the "will_modify" parameter passed to fscache_use_cookie().

Setting this to true will henceforth cause the affected object to be marked
as dirty on disk, subject to conflict resolution in the event that power
failure or a crash occurs or the filesystem operates in disconnected mode.

The dirty flag is removed when the fscache_object is discarded from memory.

A cache hook is provided to prepare for writing - and this can be used to
mark the object on disk.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

fs/cachefiles/interface.c | 65 +++++++++++++++++++++++++++++++++++++++++
fs/cachefiles/internal.h | 2 +
fs/cachefiles/xattr.c | 21 +++++++++++++
fs/fscache/cookie.c | 17 +++++++++--
fs/fscache/internal.h | 1 +
fs/fscache/obj.c | 29 +++++++++++++++---
include/linux/fscache-cache.h | 4 +++
7 files changed, 130 insertions(+), 9 deletions(-)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index b312a04f672b..457adfca5931 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -210,14 +210,78 @@ static void cachefiles_update_object(struct fscache_object *_object)
_leave("");
}

+/*
+ * Shorten the backing object to discard any dirty data and free up
+ * any unused granules.
+ */
+static bool cachefiles_shorten_object(struct cachefiles_object *object, loff_t new_size)
+{
+ struct cachefiles_cache *cache;
+ struct inode *inode;
+ struct path path;
+ loff_t i_size;
+
+ cache = container_of(object->fscache.cache,
+ struct cachefiles_cache, cache);
+ path.mnt = cache->mnt;
+ path.dentry = object->dentry;
+
+ inode = d_inode(object->dentry);
+ trace_cachefiles_trunc(object, inode, i_size_read(inode), new_size);
+ if (vfs_truncate(&path, new_size) < 0) {
+ cachefiles_io_error_obj(object, "Trunc-to-size failed");
+ cachefiles_remove_object_xattr(cache, object->dentry);
+ return false;
+ }
+
+ new_size = round_up(new_size, CACHEFILES_DIO_BLOCK_SIZE);
+ i_size = i_size_read(inode);
+ if (i_size < new_size) {
+ trace_cachefiles_trunc(object, inode, i_size, new_size);
+ if (vfs_truncate(&path, new_size) < 0) {
+ cachefiles_io_error_obj(object, "Trunc-to-dio-size failed");
+ cachefiles_remove_object_xattr(cache, object->dentry);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+/*
+ * Trim excess stored data off of an object.
+ */
+static bool cachefiles_trim_object(struct cachefiles_object *object)
+{
+ loff_t object_size;
+
+ _enter("{OBJ%x}", object->fscache.debug_id);
+
+ object_size = object->fscache.cookie->object_size;
+ if (i_size_read(d_inode(object->dentry)) <= object_size)
+ return true;
+
+ return cachefiles_shorten_object(object, object_size);
+}
+
/*
* Commit changes to the object as we drop it.
*/
static bool cachefiles_commit_object(struct cachefiles_object *object,
struct cachefiles_cache *cache)
{
+ bool update = false;
+
if (object->content_map_changed)
cachefiles_save_content_map(object);
+ if (test_and_clear_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->fscache.flags))
+ update = true;
+ if (test_and_clear_bit(FSCACHE_OBJECT_NEEDS_UPDATE, &object->fscache.flags))
+ update = true;
+ if (update) {
+ if (cachefiles_trim_object(object))
+ cachefiles_set_object_xattr(object);
+ }

if (test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags))
return cachefiles_commit_tmpfile(cache, object);
@@ -577,5 +641,6 @@ const struct fscache_cache_ops cachefiles_cache_ops = {
.shape_extent = cachefiles_shape_extent,
.read = cachefiles_read,
.write = cachefiles_write,
+ .prepare_to_write = cachefiles_prepare_to_write,
.display_object = cachefiles_display_object,
};
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index ccc8cd2b8250..487a434ddb75 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -248,7 +248,7 @@ extern int cachefiles_set_object_xattr(struct cachefiles_object *object);
extern int cachefiles_check_auxdata(struct cachefiles_object *object);
extern int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
struct dentry *dentry);
-
+extern int cachefiles_prepare_to_write(struct fscache_object *object);

/*
* error handling
diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index 22c56ca2fd0b..456301b7abb0 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -124,6 +124,8 @@ int cachefiles_set_object_xattr(struct cachefiles_object *object)
buf->zero_point = cpu_to_be64(object->fscache.cookie->zero_point);
buf->type = object->fscache.cookie->type;
buf->content = object->content_info;
+ if (test_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->fscache.flags))
+ buf->content = CACHEFILES_CONTENT_DIRTY;
if (len > 0)
memcpy(buf->data, fscache_get_aux(object->fscache.cookie), len);

@@ -184,10 +186,16 @@ int cachefiles_check_auxdata(struct cachefiles_object *object)
why = cachefiles_coherency_check_aux;
} else if (be64_to_cpu(buf->object_size) != object->fscache.cookie->object_size) {
why = cachefiles_coherency_check_objsize;
+ } else if (buf->content == CACHEFILES_CONTENT_DIRTY) {
+ // TODO: Begin conflict resolution
+ pr_warn("Dirty object in cache\n");
+ why = cachefiles_coherency_check_dirty;
} else {
object->fscache.cookie->zero_point = be64_to_cpu(buf->zero_point);
object->content_info = buf->content;
why = cachefiles_coherency_check_ok;
+ object->fscache.cookie->zero_point = be64_to_cpu(buf->zero_point);
+ object->content_info = buf->content;
ret = 0;
}

@@ -219,3 +227,16 @@ int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
_leave(" = %d", ret);
return ret;
}
+
+/*
+ * Stick a marker on the cache object to indicate that it's dirty.
+ */
+int cachefiles_prepare_to_write(struct fscache_object *_object)
+{
+ struct cachefiles_object *object =
+ container_of(_object, struct cachefiles_object, fscache);
+
+ _enter("c=%08x", object->fscache.cookie->debug_id);
+
+ return cachefiles_set_object_xattr(object);
+}
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index c0d93dc7f69f..c96cd23bcdb2 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -342,6 +342,8 @@ EXPORT_SYMBOL(__fscache_acquire_cookie);
void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
{
enum fscache_cookie_stage stage;
+ struct fscache_object *object;
+ bool write_set;

_enter("c=%08x", cookie->debug_id);

@@ -360,7 +362,7 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)

/* The lookup job holds its own active increment */
atomic_inc(&cookie->n_active);
- fscache_dispatch(cookie, NULL, 0, fscache_lookup_object);
+ fscache_dispatch(cookie, NULL, will_modify, fscache_lookup_object);
break;

case FSCACHE_COOKIE_STAGE_INITIALISING:
@@ -373,8 +375,17 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
case FSCACHE_COOKIE_STAGE_NO_DATA_YET:
case FSCACHE_COOKIE_STAGE_ACTIVE:
case FSCACHE_COOKIE_STAGE_INVALIDATING:
- // TODO: Handle will_modify
- spin_unlock(&cookie->lock);
+ if (will_modify) {
+ object = hlist_entry(cookie->backing_objects.first,
+ struct fscache_object, cookie_link);
+ write_set = test_and_set_bit(FSCACHE_OBJECT_LOCAL_WRITE,
+ &object->flags);
+ spin_unlock(&cookie->lock);
+ if (!write_set)
+ fscache_dispatch(cookie, object, 0, fscache_prepare_to_write);
+ } else {
+ spin_unlock(&cookie->lock);
+ }
break;

case FSCACHE_COOKIE_STAGE_DEAD:
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index b9cad60e3c4e..0b370d059bdf 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -134,6 +134,7 @@ extern void fscache_lookup_object(struct fscache_cookie *, struct fscache_object
extern void fscache_invalidate_object(struct fscache_cookie *, struct fscache_object *, int);
extern void fscache_drop_object(struct fscache_cookie *, struct fscache_object *, bool);
extern void fscache_discard_objects(struct fscache_cookie *, struct fscache_object *, int);
+extern void fscache_prepare_to_write(struct fscache_cookie *, struct fscache_object *, int);

/*
* object-list.c
diff --git a/fs/fscache/obj.c b/fs/fscache/obj.c
index aea4239641a9..332ba132413d 100644
--- a/fs/fscache/obj.c
+++ b/fs/fscache/obj.c
@@ -117,7 +117,8 @@ static bool fscache_wrangle_object(struct fscache_cookie *cookie,
* Create an object chain, making sure that the index chain is fully created.
*/
static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie *cookie,
- struct fscache_cache *cache)
+ struct fscache_cache *cache,
+ bool will_modify)
{
struct fscache_object *object = NULL, *parent, *xobject;

@@ -131,7 +132,7 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
spin_unlock(&cookie->lock);

/* Recurse to look up/create the parent index. */
- parent = fscache_lookup_object_chain(cookie->parent, cache);
+ parent = fscache_lookup_object_chain(cookie->parent, cache, false);
if (IS_ERR(parent))
goto error;

@@ -146,9 +147,13 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
if (!object)
goto error;

+ if (will_modify)
+ __set_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->flags);
+
xobject = fscache_attach_object(cookie, object);
if (xobject != object) {
fscache_do_put_object(object, fscache_obj_put_alloc_dup);
+ object = xobject;
goto object_exists;
}

@@ -199,7 +204,8 @@ static struct fscache_object *fscache_lookup_object_chain(struct fscache_cookie
* - this must make sure the index chain is instantiated and instantiate the
* object representation too
*/
-static void fscache_lookup_object_locked(struct fscache_cookie *cookie)
+static void fscache_lookup_object_locked(struct fscache_cookie *cookie,
+ bool will_modify)
{
struct fscache_object *object;
struct fscache_cache *cache;
@@ -217,12 +223,16 @@ static void fscache_lookup_object_locked(struct fscache_cookie *cookie)

_debug("cache %s", cache->tag->name);

- object = fscache_lookup_object_chain(cookie, cache);
+ object = fscache_lookup_object_chain(cookie, cache, will_modify);
if (!object) {
_leave(" [fail]");
return;
}

+ if (will_modify &&
+ test_and_set_bit(FSCACHE_OBJECT_LOCAL_WRITE, &object->flags))
+ fscache_prepare_to_write(cookie, object, 0);
+
fscache_do_put_object(object, fscache_obj_put);
_leave(" [done]");
}
@@ -231,7 +241,7 @@ void fscache_lookup_object(struct fscache_cookie *cookie,
struct fscache_object *object, int param)
{
down_read(&fscache_addremove_sem);
- fscache_lookup_object_locked(cookie);
+ fscache_lookup_object_locked(cookie, param);
up_read(&fscache_addremove_sem);
__fscache_unuse_cookie(cookie, NULL, NULL);
}
@@ -336,3 +346,12 @@ void fscache_discard_objects(struct fscache_cookie *cookie,
up_read(&fscache_addremove_sem);
_leave("");
}
+
+/*
+ * Prepare a cache object to be written to.
+ */
+void fscache_prepare_to_write(struct fscache_cookie *cookie,
+ struct fscache_object *object, int param)
+{
+ object->cache->ops->prepare_to_write(object);
+}
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 4fb63d8a60cd..848ced13c4ae 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -155,6 +155,9 @@ struct fscache_cache_ops {
struct fscache_io_request *req,
struct iov_iter *iter);

+ /* Prepare to write to a live cache object */
+ int (*prepare_to_write)(struct fscache_object *object);
+
/* Display object info in /proc/fs/fscache/objects */
int (*display_object)(struct seq_file *m, struct fscache_object *object);
};
@@ -183,6 +186,7 @@ struct fscache_object {
spinlock_t lock; /* state and operations lock */

unsigned long flags;
+#define FSCACHE_OBJECT_LOCAL_WRITE 1 /* T if the object is being modified locally */
#define FSCACHE_OBJECT_NEEDS_INVAL 8 /* T if object needs invalidation */
#define FSCACHE_OBJECT_NEEDS_UPDATE 9 /* T if object attrs need writing to disk */

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