[PATCH 48/67] fscache: Implement "will_modify" parameter on fscache_use_cookie()

David Howells
2021-10-18T15:02:56Z

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 cache 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@redhat.com>
---

fs/cachefiles/interface.c | 3 +++
fs/cachefiles/internal.h | 2 +-
fs/cachefiles/xattr.c | 20 ++++++++++++++++++++
fs/fscache/cookie.c | 30 +++++++++++++++++++++++++++++-
include/linux/fscache-cache.h | 3 +++
include/linux/fscache.h | 2 ++
include/trace/events/cachefiles.h | 4 ++--
7 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 751b0fec4591..96f30eba585a 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -211,6 +211,8 @@ static void cachefiles_commit_object(struct cachefiles_object *object,
{
bool update = false;

+ if (test_and_clear_bit(FSCACHE_COOKIE_LOCAL_WRITE, &object->cookie->flags))
+ update = true;
if (test_and_clear_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &object->cookie->flags))
update = true;
if (update)
@@ -461,4 +463,5 @@ const struct fscache_cache_ops cachefiles_cache_ops = {
.invalidate_cookie = cachefiles_invalidate_cookie,
.resize_cookie = cachefiles_resize_cookie,
.begin_operation = cachefiles_begin_operation,
+ .prepare_to_write = cachefiles_prepare_to_write,
};
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 1d3e37bca087..83cf2ca3a763 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -239,7 +239,7 @@ extern int cachefiles_check_auxdata(struct cachefiles_object *object,
struct file *file);
extern int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
struct dentry *dentry);
-
+extern void cachefiles_prepare_to_write(struct fscache_cookie *cookie);

/*
* error handling
diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index ba3d050a5174..30adca42883b 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -53,6 +53,8 @@ int cachefiles_set_object_xattr(struct cachefiles_object *object)
buf->zero_point = 0;
buf->type = CACHEFILES_COOKIE_TYPE_DATA;
buf->content = object->content_info;
+ if (test_bit(FSCACHE_COOKIE_LOCAL_WRITE, &object->cookie->flags))
+ buf->content = CACHEFILES_CONTENT_DIRTY;
if (len > 0)
memcpy(buf->data, fscache_get_aux(object->cookie), len);

@@ -145,3 +147,21 @@ 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.
+ */
+void cachefiles_prepare_to_write(struct fscache_cookie *cookie)
+{
+ const struct cred *saved_cred;
+ struct cachefiles_object *object = cookie->cache_priv;
+ struct cachefiles_cache *cache = object->volume->cache;
+
+ _enter("c=%08x", object->cookie->debug_id);
+
+ if (!test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags)) {
+ cachefiles_begin_secure(cache, &saved_cred);
+ cachefiles_set_object_xattr(object);
+ cachefiles_end_secure(cache, saved_cred);
+ }
+}
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 70bfbd269652..1420027cfe97 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -402,12 +402,20 @@ struct fscache_cookie *__fscache_acquire_cookie(
}
EXPORT_SYMBOL(__fscache_acquire_cookie);

+/*
+ * Prepare a cache object to be written to.
+ */
+static void fscache_prepare_to_write(struct fscache_cookie *cookie)
+{
+ cookie->volume->cache->ops->prepare_to_write(cookie);
+}
+
/*
* Look up a cookie to the cache.
*/
static void fscache_lookup_cookie(struct fscache_cookie *cookie)
{
- bool changed_stage = false, need_withdraw = false;
+ bool changed_stage = false, need_withdraw = false, prep_write = false;

_enter("");

@@ -429,6 +437,7 @@ static void fscache_lookup_cookie(struct fscache_cookie *cookie)

spin_lock(&cookie->lock);
if (cookie->stage != FSCACHE_COOKIE_STAGE_RELINQUISHING) {
+ prep_write = test_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
__fscache_set_cookie_stage(cookie, FSCACHE_COOKIE_STAGE_ACTIVE);
fscache_see_cookie(cookie, fscache_cookie_see_active);
changed_stage = true;
@@ -436,6 +445,8 @@ static void fscache_lookup_cookie(struct fscache_cookie *cookie)
spin_unlock(&cookie->lock);
if (changed_stage)
wake_up_cookie_stage(cookie);
+ if (prep_write)
+ fscache_prepare_to_write(cookie);

out:
fscache_end_cookie_access(cookie, fscache_access_lookup_cookie_end);
@@ -467,6 +478,10 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)
stage = cookie->stage;
switch (stage) {
case FSCACHE_COOKIE_STAGE_QUIESCENT:
+ if (will_modify) {
+ set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
+ set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
+ }
if (!fscache_begin_volume_access(cookie->volume,
fscache_access_lookup_cookie))
break;
@@ -484,8 +499,18 @@ void __fscache_use_cookie(struct fscache_cookie *cookie, bool will_modify)

case FSCACHE_COOKIE_STAGE_LOOKING_UP:
case FSCACHE_COOKIE_STAGE_CREATING:
+ if (will_modify)
+ set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags);
+ break;
case FSCACHE_COOKIE_STAGE_ACTIVE:
case FSCACHE_COOKIE_STAGE_INVALIDATING:
+ if (will_modify &&
+ !test_and_set_bit(FSCACHE_COOKIE_LOCAL_WRITE, &cookie->flags)) {
+ set_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
+ queue = true;
+ }
+ break;
+
case FSCACHE_COOKIE_STAGE_FAILED:
case FSCACHE_COOKIE_STAGE_WITHDRAWING:
break;
@@ -551,6 +576,8 @@ static void __fscache_cookie_worker(struct fscache_cookie *cookie)
again:
switch (READ_ONCE(cookie->stage)) {
case FSCACHE_COOKIE_STAGE_ACTIVE:
+ if (test_and_clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags))
+ fscache_prepare_to_write(cookie);
break;

case FSCACHE_COOKIE_STAGE_LOOKING_UP:
@@ -591,6 +618,7 @@ static void __fscache_cookie_worker(struct fscache_cookie *cookie)
clear_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
clear_bit(FSCACHE_COOKIE_DO_WITHDRAW, &cookie->flags);
clear_bit(FSCACHE_COOKIE_DO_COMMIT, &cookie->flags);
+ clear_bit(FSCACHE_COOKIE_DO_PREP_TO_WRITE, &cookie->flags);
set_bit(FSCACHE_COOKIE_NO_DATA_TO_READ, &cookie->flags);
fscache_set_cookie_stage(cookie, FSCACHE_COOKIE_STAGE_QUIESCENT);
break;
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 2e7265e24df6..889ae37fae0f 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -76,6 +76,9 @@ struct fscache_cache_ops {
/* Begin an operation for the netfs lib */
bool (*begin_operation)(struct netfs_cache_resources *cres,
enum fscache_want_stage want_stage);
+
+ /* Prepare to write to a live cache object */
+ void (*prepare_to_write)(struct fscache_cookie *cookie);
};

static inline enum fscache_cache_state fscache_cache_state(const struct fscache_cache *cache)
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 8148193045cd..8ab691e52cc5 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -125,10 +125,12 @@ struct fscache_cookie {
#define FSCACHE_COOKIE_NEEDS_UPDATE 4 /* T if attrs have been updated */
#define FSCACHE_COOKIE_HAS_BEEN_CACHED 5 /* T if cookie needs withdraw-on-relinq */
#define FSCACHE_COOKIE_DISABLED 6 /* T if cookie has been disabled */
+#define FSCACHE_COOKIE_LOCAL_WRITE 7 /* T if cookie has been modified locally */
#define FSCACHE_COOKIE_NACC_ELEVATED 8 /* T if n_accesses is incremented */
#define FSCACHE_COOKIE_DO_RELINQUISH 9 /* T if this cookie needs relinquishment */
#define FSCACHE_COOKIE_DO_WITHDRAW 10 /* T if this cookie needs withdrawing */
#define FSCACHE_COOKIE_DO_COMMIT 11 /* T if this cookie needs committing */
+#define FSCACHE_COOKIE_DO_PREP_TO_WRITE 12 /* T if cookie needs write preparation */

enum fscache_cookie_stage stage;
u8 advice; /* FSCACHE_ADV_* */
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index a7b31b248f2d..11447b20fc83 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -340,7 +340,7 @@ TRACE_EVENT(cachefiles_mark_inactive,
TRACE_EVENT(cachefiles_coherency,
TP_PROTO(struct cachefiles_object *obj,
ino_t ino,
- int content,
+ enum cachefiles_content content,
enum cachefiles_coherency_trace why),

TP_ARGS(obj, ino, content, why),
@@ -349,7 +349,7 @@ TRACE_EVENT(cachefiles_coherency,
TP_STRUCT__entry(
__field(unsigned int, obj )
__field(enum cachefiles_coherency_trace, why )
- __field(int, content )
+ __field(enum cachefiles_content, content )
__field(u64, ino )
),