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Subject[PATCH 1/2] printf: add support for printing symbolic error names from numbers
Date
This is an extension of the ability introduced in commit 57f5677e535b
("printf: add support for printing symbolic error names") that
made %pe consume an error valued pointer and emit a symbolic error name.

Here the same is done for numbers:

printk("%de\n", -EIO);

now emits "-EIO\n".

To keep printk flexible enough to emit an 'e' after a number the
character ` can be used which is just swallowed by *printf and ends
interpreting the format code. So

printk("%d`e\n", -5);

emits "-5e\n". (Note that the implementation of ` isn't complete, it
only works for numbers for now. It might make sense to implement the
same for %s and %p.)

For non-error valued numbers %de falls back to emit the plain number (as
%d would do).

Some runtime tests are added to cover %de.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
lib/test_printf.c | 8 ++++++++
lib/vsprintf.c | 34 +++++++++++++++++++++++++++++++++-
2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 2d9f520d2f27..a18a7742d5fe 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -13,6 +13,7 @@
#include <linux/rtc.h>
#include <linux/slab.h>
#include <linux/string.h>
+#include <linux/stringify.h>

#include <linux/bitmap.h>
#include <linux/dcache.h>
@@ -628,6 +629,8 @@ static void __init
errptr(void)
{
test("-1234", "%pe", ERR_PTR(-1234));
+ test("-4321", "%de", -4321);
+ test("-5e", "%d`e", -5);

/* Check that %pe with a non-ERR_PTR gets treated as ordinary %p. */
BUILD_BUG_ON(IS_ERR(PTR));
@@ -641,6 +644,11 @@ errptr(void)
test("[-EIO ]", "[%-8pe]", ERR_PTR(-EIO));
test("[ -EIO]", "[%8pe]", ERR_PTR(-EIO));
test("-EPROBE_DEFER", "%pe", ERR_PTR(-EPROBE_DEFER));
+
+ test("-ERESTARTSYS", "%de", -ERESTARTSYS);
+#else
+
+ test("-" __stringify(ERESTARTSYS), "%de", -ERESTARTSYS);
#endif
}

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7c488a1ce318..1bcd1ce2c319 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2637,7 +2637,39 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
num = va_arg(args, unsigned int);
}

- str = number(str, end, num, spec);
+ if (*fmt != 'e') {
+ str = number(str, end, num, spec);
+ } else {
+ unsigned long num_err = 0;
+
+ fmt++;
+
+ /*
+ * error values are negative numbers near zero.
+ * If num represents such a number, it must be
+ * big (as it is unsigned), otherwise print it
+ * as an ordinary number.
+ */
+ if (num > (unsigned long long)-UINT_MAX)
+ num_err = num;
+
+ if (IS_ENABLED(CONFIG_SYMBOLIC_ERRNAME) &&
+ IS_ERR_VALUE(num_err))
+ str = err_ptr(str, end, ERR_PTR(num), spec);
+ else
+ str = number(str, end, num, spec);
+ }
+
+ if (*fmt == '`')
+ /*
+ * When a format specifier is followed by `,
+ * this ends parsing. This way a string can be
+ * printed that has an int followed by a literal
+ * 'e' (using "%d`e") which otherwise (i.e. by
+ * using "%de") would be interpreted as request
+ * to format the int as error code.
+ */
+ ++fmt;
}
}

--
2.24.0
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