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Villemoespmladek
Villemoes
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pmladek
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printf: add support for printing symbolic error names
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>
1 parent ae88de5 commit 57f5677

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‎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
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the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
8080
gathers enough entropy. If you *really* want the address see %px below.
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82+
Error Pointers
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--------------
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::
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%pe -ENOSPC
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For printing error pointers (i.e. a pointer for which IS_ERR() is true)
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as a symbolic error name. Error values for which no symbolic name is
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known are printed in decimal, while a non-ERR_PTR passed as the
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argument to %pe gets treated as ordinary %p.
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Symbols/Function Pointers
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-------------------------
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‎include/linux/errname.h‎

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

‎lib/Kconfig.debug‎

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

‎lib/Makefile‎

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@@ -183,6 +183,7 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o
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obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
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obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
186+
obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
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obj-$(CONFIG_NLATTR) += nlattr.o
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‎lib/errname.c‎

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@@ -0,0 +1,223 @@
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// SPDX-License-Identifier: GPL-2.0
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#include <linux/build_bug.h>
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#include <linux/errno.h>
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#include <linux/errname.h>
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#include <linux/kernel.h>
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/*
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* Ensure these tables do not accidentally become gigantic if some
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* huge errno makes it in. On most architectures, the first table will
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* only have about 140 entries, but mips and parisc have more sparsely
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* allocated errnos (with EHWPOISON = 257 on parisc, and EDQUOT = 1133
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* on mips), so this wastes a bit of space on those - though we
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* special case the EDQUOT case.
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*/
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#define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = "-" #err
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static const char *names_0[] = {
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E(E2BIG),
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E(EACCES),
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E(EADDRINUSE),
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E(EADDRNOTAVAIL),
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E(EADV),
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E(EAFNOSUPPORT),
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E(EALREADY),
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E(EBADE),
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E(EBADF),
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E(EBADFD),
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E(EBADMSG),
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E(EBADR),
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E(EBADRQC),
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E(EBADSLT),
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E(EBFONT),
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E(EBUSY),
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#ifdef ECANCELLED
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E(ECANCELLED),
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#endif
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E(ECHILD),
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E(ECHRNG),
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E(ECOMM),
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E(ECONNABORTED),
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E(ECONNRESET),
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E(EDEADLOCK),
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E(EDESTADDRREQ),
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E(EDOM),
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E(EDOTDOT),
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#ifndef CONFIG_MIPS
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E(EDQUOT),
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#endif
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E(EEXIST),
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E(EFAULT),
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E(EFBIG),
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E(EHOSTDOWN),
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E(EHOSTUNREACH),
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E(EHWPOISON),
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E(EIDRM),
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E(EILSEQ),
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#ifdef EINIT
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E(EINIT),
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#endif
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E(EINPROGRESS),
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E(EINTR),
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E(EINVAL),
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E(EIO),
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E(EISCONN),
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E(EISDIR),
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E(EISNAM),
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E(EKEYEXPIRED),
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E(EKEYREJECTED),
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E(EKEYREVOKED),
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E(EL2HLT),
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E(EL2NSYNC),
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E(EL3HLT),
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E(EL3RST),
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E(ELIBACC),
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E(ELIBBAD),
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E(ELIBEXEC),
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E(ELIBMAX),
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E(ELIBSCN),
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E(ELNRNG),
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E(ELOOP),
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E(EMEDIUMTYPE),
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E(EMFILE),
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E(EMLINK),
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E(EMSGSIZE),
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E(EMULTIHOP),
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E(ENAMETOOLONG),
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E(ENAVAIL),
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E(ENETDOWN),
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E(ENETRESET),
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E(ENETUNREACH),
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E(ENFILE),
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E(ENOANO),
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E(ENOBUFS),
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E(ENOCSI),
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E(ENODATA),
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E(ENODEV),
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E(ENOENT),
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E(ENOEXEC),
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E(ENOKEY),
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E(ENOLCK),
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E(ENOLINK),
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E(ENOMEDIUM),
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E(ENOMEM),
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E(ENOMSG),
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E(ENONET),
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E(ENOPKG),
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E(ENOPROTOOPT),
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E(ENOSPC),
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E(ENOSR),
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E(ENOSTR),
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#ifdef ENOSYM
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E(ENOSYM),
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#endif
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E(ENOSYS),
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E(ENOTBLK),
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E(ENOTCONN),
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E(ENOTDIR),
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E(ENOTEMPTY),
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E(ENOTNAM),
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E(ENOTRECOVERABLE),
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E(ENOTSOCK),
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E(ENOTTY),
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E(ENOTUNIQ),
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E(ENXIO),
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E(EOPNOTSUPP),
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E(EOVERFLOW),
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E(EOWNERDEAD),
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E(EPERM),
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E(EPFNOSUPPORT),
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E(EPIPE),
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#ifdef EPROCLIM
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E(EPROCLIM),
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#endif
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E(EPROTO),
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E(EPROTONOSUPPORT),
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E(EPROTOTYPE),
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E(ERANGE),
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E(EREMCHG),
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#ifdef EREMDEV
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E(EREMDEV),
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#endif
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E(EREMOTE),
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E(EREMOTEIO),
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#ifdef EREMOTERELEASE
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E(EREMOTERELEASE),
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#endif
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E(ERESTART),
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E(ERFKILL),
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E(EROFS),
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#ifdef ERREMOTE
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E(ERREMOTE),
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#endif
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E(ESHUTDOWN),
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E(ESOCKTNOSUPPORT),
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E(ESPIPE),
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E(ESRCH),
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E(ESRMNT),
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E(ESTALE),
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E(ESTRPIPE),
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E(ETIME),
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E(ETIMEDOUT),
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E(ETOOMANYREFS),
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E(ETXTBSY),
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E(EUCLEAN),
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E(EUNATCH),
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E(EUSERS),
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E(EXDEV),
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E(EXFULL),
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E(ECANCELED), /* ECANCELLED */
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E(EAGAIN), /* EWOULDBLOCK */
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E(ECONNREFUSED), /* EREFUSED */
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E(EDEADLK), /* EDEADLOCK */
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};
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#undef E
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#define E(err) [err - 512 + BUILD_BUG_ON_ZERO(err < 512 || err > 550)] = "-" #err
177+
static const char *names_512[] = {
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E(ERESTARTSYS),
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E(ERESTARTNOINTR),
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E(ERESTARTNOHAND),
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E(ENOIOCTLCMD),
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E(ERESTART_RESTARTBLOCK),
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E(EPROBE_DEFER),
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E(EOPENSTALE),
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E(ENOPARAM),
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E(EBADHANDLE),
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E(ENOTSYNC),
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E(EBADCOOKIE),
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E(ENOTSUPP),
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E(ETOOSMALL),
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E(ESERVERFAULT),
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E(EBADTYPE),
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E(EJUKEBOX),
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E(EIOCBQUEUED),
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E(ERECALLCONFLICT),
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};
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#undef E
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static const char *__errname(unsigned err)
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{
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if (err < ARRAY_SIZE(names_0))
203+
return names_0[err];
204+
if (err >= 512 && err - 512 < ARRAY_SIZE(names_512))
205+
return names_512[err - 512];
206+
/* But why? */
207+
if (IS_ENABLED(CONFIG_MIPS) && err == EDQUOT) /* 1133 */
208+
return "-EDQUOT";
209+
return NULL;
210+
}
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212+
/*
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* errname(EIO) -> "EIO"
214+
* errname(-EIO) -> "-EIO"
215+
*/
216+
const char *errname(int err)
217+
{
218+
const char *name = __errname(abs(err));
219+
if (!name)
220+
return NULL;
221+
222+
return err > 0 ? name + 1 : name;
223+
}

‎lib/test_printf.c‎

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@@ -593,6 +593,26 @@ flags(void)
593593
kfree(cmp_buffer);
594594
}
595595

596+
static void __init
597+
errptr(void)
598+
{
599+
test("-1234", "%pe", ERR_PTR(-1234));
600+
601+
/* Check that %pe with a non-ERR_PTR gets treated as ordinary %p. */
602+
BUILD_BUG_ON(IS_ERR(PTR));
603+
test_hashed("%pe", PTR);
604+
605+
#ifdef CONFIG_SYMBOLIC_ERRNAME
606+
test("(-ENOTSOCK)", "(%pe)", ERR_PTR(-ENOTSOCK));
607+
test("(-EAGAIN)", "(%pe)", ERR_PTR(-EAGAIN));
608+
BUILD_BUG_ON(EAGAIN != EWOULDBLOCK);
609+
test("(-EAGAIN)", "(%pe)", ERR_PTR(-EWOULDBLOCK));
610+
test("[-EIO ]", "[%-8pe]", ERR_PTR(-EIO));
611+
test("[ -EIO]", "[%8pe]", ERR_PTR(-EIO));
612+
test("-EPROBE_DEFER", "%pe", ERR_PTR(-EPROBE_DEFER));
613+
#endif
614+
}
615+
596616
static void __init
597617
test_pointer(void)
598618
{
@@ -615,6 +635,7 @@ test_pointer(void)
615635
bitmap();
616636
netdev_features();
617637
flags();
638+
errptr();
618639
}
619640

620641
static void __init selftest(void)

‎lib/vsprintf.c‎

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@@ -21,6 +21,7 @@
2121
#include <linux/build_bug.h>
2222
#include <linux/clk.h>
2323
#include <linux/clk-provider.h>
24+
#include <linux/errname.h>
2425
#include <linux/module.h> /* for KSYM_SYMBOL_LEN */
2526
#include <linux/types.h>
2627
#include <linux/string.h>
@@ -613,6 +614,25 @@ static char *string_nocheck(char *buf, char *end, const char *s,
613614
return widen_string(buf, len, end, spec);
614615
}
615616

617+
static char *err_ptr(char *buf, char *end, void *ptr,
618+
struct printf_spec spec)
619+
{
620+
int err = PTR_ERR(ptr);
621+
const char *sym = errname(err);
622+
623+
if (sym)
624+
return string_nocheck(buf, end, sym, spec);
625+
626+
/*
627+
* Somebody passed ERR_PTR(-1234) or some other non-existing
628+
* Efoo - or perhaps CONFIG_SYMBOLIC_ERRNAME=n. Fall back to
629+
* printing it as its decimal representation.
630+
*/
631+
spec.flags |= SIGN;
632+
spec.base = 10;
633+
return number(buf, end, err, spec);
634+
}
635+
616636
/* Be careful: error messages must fit into the given buffer. */
617637
static char *error_string(char *buf, char *end, const char *s,
618638
struct printf_spec spec)
@@ -2187,6 +2207,11 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
21872207
return kobject_string(buf, end, ptr, spec, fmt);
21882208
case 'x':
21892209
return pointer_string(buf, end, ptr, spec);
2210+
case 'e':
2211+
/* %pe with a non-ERR_PTR gets treated as plain %p */
2212+
if (!IS_ERR(ptr))
2213+
break;
2214+
return err_ptr(buf, end, ptr, spec);
21902215
}
21912216

21922217
/* 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)
28232848
case 'f':
28242849
case 'x':
28252850
case 'K':
2851+
case 'e':
28262852
save_arg(void *);
28272853
break;
28282854
default:
@@ -2999,6 +3025,7 @@ int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf)
29993025
case 'f':
30003026
case 'x':
30013027
case 'K':
3028+
case 'e':
30023029
process = true;
30033030
break;
30043031
default:

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