Commit eb386617 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcachefs: Errcode tracepoint, documentation 



Add a tracepoint for downcasting private errors to standard errors, so
they can be recovered even when not logged; also, add some
documentation.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 150194cd

Documentation/filesystems/bcachefs/errorcodes.rst

0 → 100644
+30 −0
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.. SPDX-License-Identifier: GPL-2.0



bcachefs private error codes

----------------------------



In bcachefs, as a hard rule we do not throw or directly use standard error

codes (-EINVAL, -EBUSY, etc.). Instead, we define private error codes as needed

in fs/bcachefs/errcode.h.



This gives us much better error messages and makes debugging much easier. Any

direct uses of standard error codes you see in the source code are simply old

code that has yet to be converted - feel free to clean it up!



Private error codes may subtype another error code, this allows for grouping of

related errors that should be handled similarly (e.g. transaction restart

errors), as well as specifying which standard error code should be returned at

the bcachefs module boundary.



At the module boundary, we use bch2_err_class() to convert to a standard error

code; this also emits a trace event so that the original error code be

recovered even if it wasn't logged.



Do not reuse error codes! Generally speaking, a private error code should only

be thrown in one place. That means that when we see it in a log message we can

see, unambiguously, exactly which file and line number it was returned from.



Try to give error codes names that are as reasonably descriptive of the error

as possible. Frequently, the error will be logged at a place far removed from

where the error was generated; good names for error codes mean much more

descriptive and useful error messages.

fs/bcachefs/errcode.c

+9 −6
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 


#include "bcachefs.h"

#include "errcode.h"

#include "trace.h"



#include <linux/errname.h>
@@ -49,15 +50,17 @@ bool __bch2_err_matches(int err, int class) 
	return err == class;

}



int __bch2_err_class(int err)

int __bch2_err_class(int bch_err)

{

	err = -err;

	BUG_ON((unsigned) err >= BCH_ERR_MAX);

	int std_err = -bch_err;

	BUG_ON((unsigned) std_err >= BCH_ERR_MAX);



	while (err >= BCH_ERR_START && bch2_errcode_parents[err - BCH_ERR_START])

		err = bch2_errcode_parents[err - BCH_ERR_START];

	while (std_err >= BCH_ERR_START && bch2_errcode_parents[std_err - BCH_ERR_START])

		std_err = bch2_errcode_parents[std_err - BCH_ERR_START];



	trace_error_downcast(bch_err, std_err, _RET_IP_);



	return -err;

	return -std_err;

}



const char *bch2_blk_status_to_str(blk_status_t status)

fs/bcachefs/errcode.h

+1 −0
Original line number Diff line number Diff line
@@ -78,6 +78,7 @@ 
	x(ENOMEM,			ENOMEM_fs_name_alloc)			\

	x(ENOMEM,			ENOMEM_fs_other_alloc)			\

	x(ENOMEM,			ENOMEM_dev_alloc)			\

	x(ENOMEM,			ENOMEM_disk_accounting)			\

	x(ENOSPC,			ENOSPC_disk_reservation)		\

	x(ENOSPC,			ENOSPC_bucket_alloc)			\

	x(ENOSPC,			ENOSPC_disk_label_add)			\

fs/bcachefs/trace.h

+19 −0
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@@ -1431,6 +1431,25 @@ DEFINE_EVENT(fs_str, data_update, 
	TP_ARGS(c, str)

);



TRACE_EVENT(error_downcast,

	TP_PROTO(int bch_err, int std_err, unsigned long ip),

	TP_ARGS(bch_err, std_err, ip),



	TP_STRUCT__entry(

		__array(char,		bch_err, 32		)

		__array(char,		std_err, 32		)

		__array(char,		ip, 32			)

	),



	TP_fast_assign(

		strscpy(__entry->bch_err, bch2_err_str(bch_err), sizeof(__entry->bch_err));

		strscpy(__entry->std_err, bch2_err_str(std_err), sizeof(__entry->std_err));

		snprintf(__entry->ip, sizeof(__entry->ip), "%ps", (void *) ip);

	),



	TP_printk("%s -> %s %s", __entry->bch_err, __entry->std_err, __entry->ip)

);



#endif /* _TRACE_BCACHEFS_H */



/* This part must be outside protection */