Add a tracepoint to trace truncation operations.

Signed-off-by: David Howells <dhowe...@redhat.com>
---

 fs/cachefiles/interface.c         |    9 +++++++-
 include/trace/events/cachefiles.h |   40 +++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 4edb3a09932a..8f98e5c27d66 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -341,9 +341,16 @@ static void cachefiles_invalidate_object(struct 
cachefiles_object *object)
                ASSERT(d_is_reg(file->f_path.dentry));
 
                cachefiles_begin_secure(cache, &saved_cred);
+               trace_cachefiles_trunc(object, file_inode(file),
+                                      i_size_read(file_inode(file)), 0,
+                                      cachefiles_trunc_invalidate);
                ret = vfs_truncate(&file->f_path, 0);
-               if (ret == 0)
+               if (ret == 0) {
+                       trace_cachefiles_trunc(object, file_inode(file),
+                                              0, ni_size,
+                                              cachefiles_trunc_set_size);
                        ret = vfs_truncate(&file->f_path, ni_size);
+               }
                cachefiles_end_secure(cache, saved_cred);
 
                if (ret != 0) {
diff --git a/include/trace/events/cachefiles.h 
b/include/trace/events/cachefiles.h
index 6e9f6462833d..09d76c160451 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -37,6 +37,11 @@ enum cachefiles_coherency_trace {
        cachefiles_coherency_set_ok,
 };
 
+enum cachefiles_trunc_trace {
+       cachefiles_trunc_invalidate,
+       cachefiles_trunc_set_size,
+};
+
 #endif
 
 /*
@@ -72,6 +77,10 @@ enum cachefiles_coherency_trace {
        EM(cachefiles_coherency_set_fail,       "SET fail")             \
        E_(cachefiles_coherency_set_ok,         "SET ok  ")
 
+#define cachefiles_trunc_traces                                                
\
+       EM(cachefiles_trunc_invalidate,         "INVAL ")               \
+       E_(cachefiles_trunc_set_size,           "SETSIZ")
+
 /*
  * Export enum symbols via userspace.
  */
@@ -83,6 +92,7 @@ enum cachefiles_coherency_trace {
 cachefiles_obj_kill_traces;
 cachefiles_obj_ref_traces;
 cachefiles_coherency_traces;
+cachefiles_trunc_traces;
 
 /*
  * Now redefine the EM() and E_() macros to map the enums to the strings that
@@ -292,6 +302,36 @@ TRACE_EVENT(cachefiles_coherency,
                      __entry->content)
            );
 
+TRACE_EVENT(cachefiles_trunc,
+           TP_PROTO(struct cachefiles_object *obj, struct inode *backer,
+                    loff_t from, loff_t to, enum cachefiles_trunc_trace why),
+
+           TP_ARGS(obj, backer, from, to, why),
+
+           TP_STRUCT__entry(
+                   __field(unsigned int,                       obj     )
+                   __field(unsigned int,                       backer  )
+                   __field(enum cachefiles_trunc_trace,        why     )
+                   __field(loff_t,                             from    )
+                   __field(loff_t,                             to      )
+                            ),
+
+           TP_fast_assign(
+                   __entry->obj        = obj->debug_id;
+                   __entry->backer     = backer->i_ino;
+                   __entry->from       = from;
+                   __entry->to         = to;
+                   __entry->why        = why;
+                          ),
+
+           TP_printk("o=%08x b=%08x %s l=%llx->%llx",
+                     __entry->obj,
+                     __entry->backer,
+                     __print_symbolic(__entry->why, cachefiles_trunc_traces),
+                     __entry->from,
+                     __entry->to)
+           );
+
 #endif /* _TRACE_CACHEFILES_H */
 
 /* This part must be outside protection */


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