cachefiles: Add a couple of tracepoints for logging errors

Add two trace points to log errors, one for vfs operations like mkdir or
create, and one for I/O operations, like read, write or truncate.

Also add the beginnings of a struct that is going to represent a data file
and place a debugging ID in it for the tracepoints to record.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819625632.215744.17907340966178411033.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906926297.143852.18267924605548658911.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967135390.1823006.2512120406360156424.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021534029.640689.1875723624947577095.stgit@warthog.procyon.org.uk/ # v4

fs/cachefiles/internal.h

@@ -62,6 +62,7 @@ struct cachefiles_cache {
 	char				*tag;		/* cache binding tag */
 };
 
+#include <trace/events/cachefiles.h>
 
 /*
  * error_inject.c

include/trace/events/cachefiles.h

@@ -18,11 +18,49 @@
 #ifndef __CACHEFILES_DECLARE_TRACE_ENUMS_ONCE_ONLY
 #define __CACHEFILES_DECLARE_TRACE_ENUMS_ONCE_ONLY
 
+enum cachefiles_error_trace {
+	cachefiles_trace_fallocate_error,
+	cachefiles_trace_getxattr_error,
+	cachefiles_trace_link_error,
+	cachefiles_trace_lookup_error,
+	cachefiles_trace_mkdir_error,
+	cachefiles_trace_notify_change_error,
+	cachefiles_trace_open_error,
+	cachefiles_trace_read_error,
+	cachefiles_trace_remxattr_error,
+	cachefiles_trace_rename_error,
+	cachefiles_trace_seek_error,
+	cachefiles_trace_setxattr_error,
+	cachefiles_trace_statfs_error,
+	cachefiles_trace_tmpfile_error,
+	cachefiles_trace_trunc_error,
+	cachefiles_trace_unlink_error,
+	cachefiles_trace_write_error,
+};
+
 #endif
 
 /*
  * Define enum -> string mappings for display.
  */
+#define cachefiles_error_traces						\
+	EM(cachefiles_trace_fallocate_error,	"fallocate")		\
+	EM(cachefiles_trace_getxattr_error,	"getxattr")		\
+	EM(cachefiles_trace_link_error,		"link")			\
+	EM(cachefiles_trace_lookup_error,	"lookup")		\
+	EM(cachefiles_trace_mkdir_error,	"mkdir")		\
+	EM(cachefiles_trace_notify_change_error, "notify_change")	\
+	EM(cachefiles_trace_open_error,		"open")			\
+	EM(cachefiles_trace_read_error,		"read")			\
+	EM(cachefiles_trace_remxattr_error,	"remxattr")		\
+	EM(cachefiles_trace_rename_error,	"rename")		\
+	EM(cachefiles_trace_seek_error,		"seek")			\
+	EM(cachefiles_trace_setxattr_error,	"setxattr")		\
+	EM(cachefiles_trace_statfs_error,	"statfs")		\
+	EM(cachefiles_trace_tmpfile_error,	"tmpfile")		\
+	EM(cachefiles_trace_trunc_error,	"trunc")		\
+	EM(cachefiles_trace_unlink_error,	"unlink")		\
+	E_(cachefiles_trace_write_error,	"write")
 
 
 /*
@@ -33,6 +71,8 @@
 #define EM(a, b) TRACE_DEFINE_ENUM(a);
 #define E_(a, b) TRACE_DEFINE_ENUM(a);
 
+cachefiles_error_traces;
+
 /*
  * Now redefine the EM() and E_() macros to map the enums to the strings that
  * will be printed in the output.
@@ -43,6 +83,60 @@
 #define E_(a, b)	{ a, b }
 
 
+TRACE_EVENT(cachefiles_vfs_error,
+	    TP_PROTO(struct cachefiles_object *obj, struct inode *backer,
+		     int error, enum cachefiles_error_trace where),
+
+	    TP_ARGS(obj, backer, error, where),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,			obj	)
+		    __field(unsigned int,			backer	)
+		    __field(enum cachefiles_error_trace,	where	)
+		    __field(short,				error	)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->obj	= obj ? obj->debug_id : 0;
+		    __entry->backer	= backer->i_ino;
+		    __entry->error	= error;
+		    __entry->where	= where;
+			   ),
+
+	    TP_printk("o=%08x b=%08x %s e=%d",
+		      __entry->obj,
+		      __entry->backer,
+		      __print_symbolic(__entry->where, cachefiles_error_traces),
+		      __entry->error)
+	    );
+
+TRACE_EVENT(cachefiles_io_error,
+	    TP_PROTO(struct cachefiles_object *obj, struct inode *backer,
+		     int error, enum cachefiles_error_trace where),
+
+	    TP_ARGS(obj, backer, error, where),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,			obj	)
+		    __field(unsigned int,			backer	)
+		    __field(enum cachefiles_error_trace,	where	)
+		    __field(short,				error	)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->obj	= obj ? obj->debug_id : 0;
+		    __entry->backer	= backer->i_ino;
+		    __entry->error	= error;
+		    __entry->where	= where;
+			   ),
+
+	    TP_printk("o=%08x b=%08x %s e=%d",
+		      __entry->obj,
+		      __entry->backer,
+		      __print_symbolic(__entry->where, cachefiles_error_traces),
+		      __entry->error)
+	    );
+
 #endif /* _TRACE_CACHEFILES_H */
 
 /* This part must be outside protection */