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printf: add support for printing symbolic error names

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It has been suggested several times to extend vsnprintf() to be able
to convert the numeric value of ENOSPC to print "ENOSPC". This
implements that as a %p extension: With %pe, one can do

  if (IS_ERR(foo)) {
    pr_err("Sorry, can't do that: %pe\n", foo);
    return PTR_ERR(foo);
  }

instead of what is seen in quite a few places in the kernel:

  if (IS_ERR(foo)) {
    pr_err("Sorry, can't do that: %ld\n", PTR_ERR(foo));
    return PTR_ERR(foo);
  }

If the value passed to %pe is an ERR_PTR, but the library function
errname() added here doesn't know about the value, the value is simply
printed in decimal. If the value passed to %pe is not an ERR_PTR, we
treat it as an ordinary %p and thus print the hashed value (passing
non-ERR_PTR values to %pe indicates a bug in the caller, but we can't
do much about that).

With my embedded hat on, and because it's not very invasive to do,
I've made it possible to remove this. The errname() function and
associated lookup tables take up about 3K. For most, that's probably
quite acceptable and a price worth paying for more readable
dmesg (once this starts getting used), while for those that disable
printk() it's of very little use - I don't see a
procfs/sysfs/seq_printf() file reasonably making use of this - and
they clearly want to squeeze vmlinux as much as possible. Hence the
default y if PRINTK.

The symbols to include have been found by massaging the output of

  find arch include -iname 'errno*.h' | xargs grep -E 'define\s*E'

In the cases where some common aliasing exists
(e.g. EAGAIN=EWOULDBLOCK on all platforms, EDEADLOCK=EDEADLK on most),
I've moved the more popular one (in terms of 'git grep -w Efoo | wc)
to the bottom so that one takes precedence.

Link: http://lkml.kernel.org/r/20191015190706.15989-1-linux@rasmusvillemoes.dk
To: "Jonathan Corbet" <corbet@lwn.net>
To: linux-kernel@vger.kernel.org
Cc: "Andy Shevchenko" <andy.shevchenko@gmail.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>
Cc: "Joe Perches" <joe@perches.com>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
[andy.shevchenko@gmail.com: use abs()]
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Rasmus Villemoes 2019-10-15 21:07:05 +02:00 committed by Petr Mladek
parent ae88de56a1
commit 57f5677e53
7 changed files with 309 additions and 0 deletions
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12
Documentation/core-api/printk-formats.rst
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@ -79,6 +79,18 @@ has the added benefit of providing a unique identifier. On 64-bit machines
the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
gathers enough entropy. If you *really* want the address see %px below.
Error Pointers
--------------
::
%pe -ENOSPC
For printing error pointers (i.e. a pointer for which IS_ERR() is true)
as a symbolic error name. Error values for which no symbolic name is
known are printed in decimal, while a non-ERR_PTR passed as the
argument to %pe gets treated as ordinary %p.
Symbols/Function Pointers
-------------------------

16
include/linux/errname.h Normal file
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@ -0,0 +1,16 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_ERRNAME_H
#define _LINUX_ERRNAME_H
#include <linux/stddef.h>
#ifdef CONFIG_SYMBOLIC_ERRNAME
const char *errname(int err);
#else
static inline const char *errname(int err)
{
return NULL;
}
#endif
#endif /* _LINUX_ERRNAME_H */

9
lib/Kconfig.debug
View File

@ -164,6 +164,15 @@ config DYNAMIC_DEBUG
See Documentation/admin-guide/dynamic-debug-howto.rst for additional
information.
config SYMBOLIC_ERRNAME
bool "Support symbolic error names in printf"
default y if PRINTK
help
If you say Y here, the kernel's printf implementation will
be able to print symbolic error names such as ENOSPC instead
of the number 28. It makes the kernel image slightly larger
(about 3KB), but can make the kernel logs easier to read.
endmenu # "printk and dmesg options"
menu "Compile-time checks and compiler options"

1
lib/Makefile
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@ -183,6 +183,7 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o
obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
obj-$(CONFIG_NLATTR) += nlattr.o

223
lib/errname.c Normal file
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@ -0,0 +1,223 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/build_bug.h>
#include <linux/errno.h>
#include <linux/errname.h>
#include <linux/kernel.h>
/*
* Ensure these tables do not accidentally become gigantic if some
* huge errno makes it in. On most architectures, the first table will
* only have about 140 entries, but mips and parisc have more sparsely
* allocated errnos (with EHWPOISON = 257 on parisc, and EDQUOT = 1133
* on mips), so this wastes a bit of space on those - though we
* special case the EDQUOT case.
*/
#define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = "-" #err
static const char *names_0[] = {
E(E2BIG),
E(EACCES),
E(EADDRINUSE),
E(EADDRNOTAVAIL),
E(EADV),
E(EAFNOSUPPORT),
E(EALREADY),
E(EBADE),
E(EBADF),
E(EBADFD),
E(EBADMSG),
E(EBADR),
E(EBADRQC),
E(EBADSLT),
E(EBFONT),
E(EBUSY),
#ifdef ECANCELLED
E(ECANCELLED),
#endif
E(ECHILD),
E(ECHRNG),
E(ECOMM),
E(ECONNABORTED),
E(ECONNRESET),
E(EDEADLOCK),
E(EDESTADDRREQ),
E(EDOM),
E(EDOTDOT),
#ifndef CONFIG_MIPS
E(EDQUOT),
#endif
E(EEXIST),
E(EFAULT),
E(EFBIG),
E(EHOSTDOWN),
E(EHOSTUNREACH),
E(EHWPOISON),
E(EIDRM),
E(EILSEQ),
#ifdef EINIT
E(EINIT),
#endif
E(EINPROGRESS),
E(EINTR),
E(EINVAL),
E(EIO),
E(EISCONN),
E(EISDIR),
E(EISNAM),
E(EKEYEXPIRED),
E(EKEYREJECTED),
E(EKEYREVOKED),
E(EL2HLT),
E(EL2NSYNC),
E(EL3HLT),
E(EL3RST),
E(ELIBACC),
E(ELIBBAD),
E(ELIBEXEC),
E(ELIBMAX),
E(ELIBSCN),
E(ELNRNG),
E(ELOOP),
E(EMEDIUMTYPE),
E(EMFILE),
E(EMLINK),
E(EMSGSIZE),
E(EMULTIHOP),
E(ENAMETOOLONG),
E(ENAVAIL),
E(ENETDOWN),
E(ENETRESET),
E(ENETUNREACH),
E(ENFILE),
E(ENOANO),
E(ENOBUFS),
E(ENOCSI),
E(ENODATA),
E(ENODEV),
E(ENOENT),
E(ENOEXEC),
E(ENOKEY),
E(ENOLCK),
E(ENOLINK),
E(ENOMEDIUM),
E(ENOMEM),
E(ENOMSG),
E(ENONET),
E(ENOPKG),
E(ENOPROTOOPT),
E(ENOSPC),
E(ENOSR),
E(ENOSTR),
#ifdef ENOSYM
E(ENOSYM),
#endif
E(ENOSYS),
E(ENOTBLK),
E(ENOTCONN),
E(ENOTDIR),
E(ENOTEMPTY),
E(ENOTNAM),
E(ENOTRECOVERABLE),
E(ENOTSOCK),
E(ENOTTY),
E(ENOTUNIQ),
E(ENXIO),
E(EOPNOTSUPP),
E(EOVERFLOW),
E(EOWNERDEAD),
E(EPERM),
E(EPFNOSUPPORT),
E(EPIPE),
#ifdef EPROCLIM
E(EPROCLIM),
#endif
E(EPROTO),
E(EPROTONOSUPPORT),
E(EPROTOTYPE),
E(ERANGE),
E(EREMCHG),
#ifdef EREMDEV
E(EREMDEV),
#endif
E(EREMOTE),
E(EREMOTEIO),
#ifdef EREMOTERELEASE
E(EREMOTERELEASE),
#endif
E(ERESTART),
E(ERFKILL),
E(EROFS),
#ifdef ERREMOTE
E(ERREMOTE),
#endif
E(ESHUTDOWN),
E(ESOCKTNOSUPPORT),
E(ESPIPE),
E(ESRCH),
E(ESRMNT),
E(ESTALE),
E(ESTRPIPE),
E(ETIME),
E(ETIMEDOUT),
E(ETOOMANYREFS),
E(ETXTBSY),
E(EUCLEAN),
E(EUNATCH),
E(EUSERS),
E(EXDEV),
E(EXFULL),
E(ECANCELED), /* ECANCELLED */
E(EAGAIN), /* EWOULDBLOCK */
E(ECONNREFUSED), /* EREFUSED */
E(EDEADLK), /* EDEADLOCK */
};
#undef E
#define E(err) [err - 512 + BUILD_BUG_ON_ZERO(err < 512 || err > 550)] = "-" #err
static const char *names_512[] = {
E(ERESTARTSYS),
E(ERESTARTNOINTR),
E(ERESTARTNOHAND),
E(ENOIOCTLCMD),
E(ERESTART_RESTARTBLOCK),
E(EPROBE_DEFER),
E(EOPENSTALE),
E(ENOPARAM),
E(EBADHANDLE),
E(ENOTSYNC),
E(EBADCOOKIE),
E(ENOTSUPP),
E(ETOOSMALL),
E(ESERVERFAULT),
E(EBADTYPE),
E(EJUKEBOX),
E(EIOCBQUEUED),
E(ERECALLCONFLICT),
};
#undef E
static const char *__errname(unsigned err)
{
if (err < ARRAY_SIZE(names_0))
return names_0[err];
if (err >= 512 && err - 512 < ARRAY_SIZE(names_512))
return names_512[err - 512];
/* But why? */
if (IS_ENABLED(CONFIG_MIPS) && err == EDQUOT) /* 1133 */
return "-EDQUOT";
return NULL;
}
/*
* errname(EIO) -> "EIO"
* errname(-EIO) -> "-EIO"
*/
const char *errname(int err)
{
const char *name = __errname(abs(err));
if (!name)
return NULL;
return err > 0 ? name + 1 : name;
}

21
lib/test_printf.c
View File

@ -593,6 +593,26 @@ flags(void)
kfree(cmp_buffer);
}
static void __init
errptr(void)
{
test("-1234", "%pe", ERR_PTR(-1234));
/* Check that %pe with a non-ERR_PTR gets treated as ordinary %p. */
BUILD_BUG_ON(IS_ERR(PTR));
test_hashed("%pe", PTR);
#ifdef CONFIG_SYMBOLIC_ERRNAME
test("(-ENOTSOCK)", "(%pe)", ERR_PTR(-ENOTSOCK));
test("(-EAGAIN)", "(%pe)", ERR_PTR(-EAGAIN));
BUILD_BUG_ON(EAGAIN != EWOULDBLOCK);
test("(-EAGAIN)", "(%pe)", ERR_PTR(-EWOULDBLOCK));
test("[-EIO ]", "[%-8pe]", ERR_PTR(-EIO));
test("[ -EIO]", "[%8pe]", ERR_PTR(-EIO));
test("-EPROBE_DEFER", "%pe", ERR_PTR(-EPROBE_DEFER));
#endif
}
static void __init
test_pointer(void)
{
@ -615,6 +635,7 @@ test_pointer(void)
bitmap();
netdev_features();
flags();
errptr();
}
static void __init selftest(void)

27
lib/vsprintf.c
View File

@ -21,6 +21,7 @@
#include <linux/build_bug.h>
#include <linux/clk.h>
#include <linux/clk-provider.h>
#include <linux/errname.h>
#include <linux/module.h> /* for KSYM_SYMBOL_LEN */
#include <linux/types.h>
#include <linux/string.h>
@ -613,6 +614,25 @@ static char *string_nocheck(char *buf, char *end, const char *s,
return widen_string(buf, len, end, spec);
}
static char *err_ptr(char *buf, char *end, void *ptr,
struct printf_spec spec)
{
int err = PTR_ERR(ptr);
const char *sym = errname(err);
if (sym)
return string_nocheck(buf, end, sym, spec);
/*
* Somebody passed ERR_PTR(-1234) or some other non-existing
* Efoo - or perhaps CONFIG_SYMBOLIC_ERRNAME=n. Fall back to
* printing it as its decimal representation.
*/
spec.flags |= SIGN;
spec.base = 10;
return number(buf, end, err, spec);
}
/* Be careful: error messages must fit into the given buffer. */
static char *error_string(char *buf, char *end, const char *s,
struct printf_spec spec)
@ -2187,6 +2207,11 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return kobject_string(buf, end, ptr, spec, fmt);
case 'x':
return pointer_string(buf, end, ptr, spec);
case 'e':
/* %pe with a non-ERR_PTR gets treated as plain %p */
if (!IS_ERR(ptr))
break;
return err_ptr(buf, end, ptr, spec);
}
/* default is to _not_ leak addresses, hash before printing */
@ -2823,6 +2848,7 @@ int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args)
case 'f':
case 'x':
case 'K':
case 'e':
save_arg(void *);
break;
default:
@ -2999,6 +3025,7 @@ int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf)
case 'f':
case 'x':
case 'K':
case 'e':
process = true;
break;
default: