lib/vsprintf: add %*pE[achnops] format specifier

This allows user to print a given buffer as an escaped string.  The
rules are applied according to an optional mix of flags provided by
additional format letters.

For example, if the given buffer is:

    1b 62 20 5c 43 07 22 90 0d 5d

The result strings would be:
    %*pE            "\eb \C\a"\220\r]"
    %*pEhp          "\x1bb \C\x07"\x90\x0d]"
    %*pEa           "\e\142\040\\\103\a\042\220\r\135"

Please, read Documentation/printk-formats.txt and lib/string_helpers.c
kernel documentation to get further information.

[akpm@linux-foundation.org: tidy up comment layout, per Joe]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Joe Perches <joe@perches.com>
Cc: "John W . Linville" <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 103 insertions, 0 deletions

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index b4498218c474..5a615c14f75d 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -70,6 +70,38 @@ DMA addresses types dma_addr_t:
         For printing a dma_addr_t type which can vary based on build options,
         regardless of the width of the CPU data path. Passed by reference.
 
+Raw buffer as an escaped string:
+
+        %*pE[achnops]
+
+        For printing raw buffer as an escaped string. For the following buffer
+
+                1b 62 20 5c 43 07 22 90 0d 5d
+
+        few examples show how the conversion would be done (the result string
+        without surrounding quotes):
+
+                %*pE            "\eb \C\a"\220\r]"
+                %*pEhp          "\x1bb \C\x07"\x90\x0d]"
+                %*pEa           "\e\142\040\\\103\a\042\220\r\135"
+
+        The conversion rules are applied according to an optional combination
+        of flags (see string_escape_mem() kernel documentation for the
+        details):
+                a - ESCAPE_ANY
+                c - ESCAPE_SPECIAL
+                h - ESCAPE_HEX
+                n - ESCAPE_NULL
+                o - ESCAPE_OCTAL
+                p - ESCAPE_NP
+                s - ESCAPE_SPACE
+        By default ESCAPE_ANY_NP is used.
+
+        ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
+        printing SSIDs.
+
+        If field width is omitted the 1 byte only will be escaped.
+
 Raw buffer as a hex string:
         %*ph    00 01 02  ...  3f
         %*phC   00:01:02: ... :3f
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index ba3cd0a35640..ec337f64f52d 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -33,6 +33,7 @@
 #include <asm/page.h>           /* for PAGE_SIZE */
 #include <asm/sections.h>       /* for dereference_function_descriptor() */
 
+#include <linux/string_helpers.h>
 #include "kstrtox.h"
 
 /**
@@ -1101,6 +1102,62 @@ char *ip4_addr_string_sa(char *buf, char *end, const struct sockaddr_in *sa,
 }
 
 static noinline_for_stack
+char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
+                     const char *fmt)
+{
+        bool found = true;
+        int count = 1;
+        unsigned int flags = 0;
+        int len;
+
+        if (spec.field_width == 0)
+                return buf;                             /* nothing to print */
+
+        if (ZERO_OR_NULL_PTR(addr))
+                return string(buf, end, NULL, spec);    /* NULL pointer */
+
+
+        do {
+                switch (fmt[count++]) {
+                case 'a':
+                        flags |= ESCAPE_ANY;
+                        break;
+                case 'c':
+                        flags |= ESCAPE_SPECIAL;
+                        break;
+                case 'h':
+                        flags |= ESCAPE_HEX;
+                        break;
+                case 'n':
+                        flags |= ESCAPE_NULL;
+                        break;
+                case 'o':
+                        flags |= ESCAPE_OCTAL;
+                        break;
+                case 'p':
+                        flags |= ESCAPE_NP;
+                        break;
+                case 's':
+                        flags |= ESCAPE_SPACE;
+                        break;
+                default:
+                        found = false;
+                        break;
+                }
+        } while (found);
+
+        if (!flags)
+                flags = ESCAPE_ANY_NP;
+
+        len = spec.field_width < 0 ? 1 : spec.field_width;
+
+        /* Ignore the error. We print as many characters as we can */
+        string_escape_mem(addr, len, &buf, end - buf, flags, NULL);
+
+        return buf;
+}
+
+static noinline_for_stack
 char *uuid_string(char *buf, char *end, const u8 *addr,
                   struct printf_spec spec, const char *fmt)
 {
@@ -1221,6 +1278,17 @@ int kptr_restrict __read_mostly;
  * - '[Ii][4S][hnbl]' IPv4 addresses in host, network, big or little endian order
  * - 'I[6S]c' for IPv6 addresses printed as specified by
  *       http://tools.ietf.org/html/rfc5952
+ * - 'E[achnops]' For an escaped buffer, where rules are defined by combination
+ *                of the following flags (see string_escape_mem() for the
+ *                details):
+ *                  a - ESCAPE_ANY
+ *                  c - ESCAPE_SPECIAL
+ *                  h - ESCAPE_HEX
+ *                  n - ESCAPE_NULL
+ *                  o - ESCAPE_OCTAL
+ *                  p - ESCAPE_NP
+ *                  s - ESCAPE_SPACE
+ *                By default ESCAPE_ANY_NP is used.
  * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form
  *       "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
  *       Options for %pU are:
@@ -1321,6 +1389,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
                         }}
                 }
                 break;
+        case 'E':
+                return escaped_string(buf, end, ptr, spec, fmt);
         case 'U':
                 return uuid_string(buf, end, ptr, spec, fmt);
         case 'V':
@@ -1633,6 +1703,7 @@ qualifier:
  * %piS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address
  * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
  *   case.
+ * %*pE[achnops] print an escaped buffer
  * %*ph[CDN] a variable-length hex string with a separator (supports up to 64
  *           bytes of the input)
  * %n is ignored