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Subject[PATCH v3 2/3] lib/string_helpers.c: Refactor string_escape_mem
Date
When printf is given the format specifier %pE, it needs a way of
obtaining the total output size that would be generated if the buffer
was large enough, and string_escape_mem doesn't easily provide
that. This is a refactorization of string_escape_mem in preparation of
changing its external API to provide that information.

The somewhat ugly 'goto skip;'s and subsequent seemingly redundant
conditionals are to make the following patch touch as little as
possible in string_helpers.c while still preserving the current
behaviour of never outputting partial escape sequences. That behaviour
must also change for %pE to work as one expects from every other
printf specifier.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
lib/string_helpers.c | 202 +++++++++++++++++++++++----------------------------
1 file changed, 90 insertions(+), 112 deletions(-)

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 58b78ba57439..7e2fef1eb40e 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -243,29 +243,21 @@ int string_unescape(char *src, char *dst, size_t size, unsigned int flags)
}
EXPORT_SYMBOL(string_unescape);

-static int escape_passthrough(unsigned char c, char **dst, size_t *osz)
+static bool escape_passthrough(unsigned char c, char **dst, char *end)
{
char *out = *dst;

- if (*osz < 1)
- return -ENOMEM;
-
- *out++ = c;
-
- *dst = out;
- *osz -= 1;
-
- return 1;
+ if (out < end)
+ *out = c;
+ *dst = out + 1;
+ return true;
}

-static int escape_space(unsigned char c, char **dst, size_t *osz)
+static bool escape_space(unsigned char c, char **dst, char *end)
{
char *out = *dst;
unsigned char to;

- if (*osz < 2)
- return -ENOMEM;
-
switch (c) {
case '\n':
to = 'n';
@@ -283,26 +275,26 @@ static int escape_space(unsigned char c, char **dst, size_t *osz)
to = 'f';
break;
default:
- return 0;
+ return false;
}

- *out++ = '\\';
- *out++ = to;
-
- *dst = out;
- *osz -= 2;
+ if (out + 1 >= end)
+ goto skip;
+ if (out + 0 < end)
+ out[0] = '\\';
+ if (out + 1 < end)
+ out[1] = to;

- return 1;
+skip:
+ *dst = out + 2;
+ return true;
}

-static int escape_special(unsigned char c, char **dst, size_t *osz)
+static bool escape_special(unsigned char c, char **dst, char *end)
{
char *out = *dst;
unsigned char to;

- if (*osz < 2)
- return -ENOMEM;
-
switch (c) {
case '\\':
to = '\\';
@@ -314,71 +306,78 @@ static int escape_special(unsigned char c, char **dst, size_t *osz)
to = 'e';
break;
default:
- return 0;
+ return false;
}

- *out++ = '\\';
- *out++ = to;
-
- *dst = out;
- *osz -= 2;
+ if (out + 1 >= end)
+ goto skip;
+ if (out + 0 < end)
+ out[0] = '\\';
+ if (out + 1 < end)
+ out[1] = to;

- return 1;
+skip:
+ *dst = out + 2;
+ return true;
}

-static int escape_null(unsigned char c, char **dst, size_t *osz)
+static bool escape_null(unsigned char c, char **dst, char *end)
{
char *out = *dst;

- if (*osz < 2)
- return -ENOMEM;
-
if (c)
- return 0;
-
- *out++ = '\\';
- *out++ = '0';
+ return false;

- *dst = out;
- *osz -= 2;
+ if (out + 1 >= end)
+ goto skip;
+ if (out + 0 < end)
+ out[0] = '\\';
+ if (out + 1 < end)
+ out[1] = '0';

- return 1;
+skip:
+ *dst = out + 2;
+ return true;
}

-static int escape_octal(unsigned char c, char **dst, size_t *osz)
+static bool escape_octal(unsigned char c, char **dst, char *end)
{
char *out = *dst;

- if (*osz < 4)
- return -ENOMEM;
-
- *out++ = '\\';
- *out++ = ((c >> 6) & 0x07) + '0';
- *out++ = ((c >> 3) & 0x07) + '0';
- *out++ = ((c >> 0) & 0x07) + '0';
-
- *dst = out;
- *osz -= 4;
-
- return 1;
+ if (out + 3 >= end)
+ goto skip;
+ if (out + 0 < end)
+ out[0] = '\\';
+ if (out + 1 < end)
+ out[1] = ((c >> 6) & 0x07) + '0';
+ if (out + 2 < end)
+ out[2] = ((c >> 3) & 0x07) + '0';
+ if (out + 3 < end)
+ out[3] = ((c >> 0) & 0x07) + '0';
+
+skip:
+ *dst = out + 4;
+ return true;
}

-static int escape_hex(unsigned char c, char **dst, size_t *osz)
+static bool escape_hex(unsigned char c, char **dst, char *end)
{
char *out = *dst;

- if (*osz < 4)
- return -ENOMEM;
-
- *out++ = '\\';
- *out++ = 'x';
- *out++ = hex_asc_hi(c);
- *out++ = hex_asc_lo(c);
-
- *dst = out;
- *osz -= 4;
-
- return 1;
+ if (out + 3 >= end)
+ goto skip;
+ if (out + 0 < end)
+ out[0] = '\\';
+ if (out + 1 < end)
+ out[1] = 'x';
+ if (out + 2 < end)
+ out[2] = hex_asc_hi(c);
+ if (out + 3 < end)
+ out[3] = hex_asc_lo(c);
+
+skip:
+ *dst = out + 4;
+ return true;
}

/**
@@ -440,9 +439,10 @@ static int escape_hex(unsigned char c, char **dst, size_t *osz)
int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
unsigned int flags, const char *esc)
{
- char *out = *dst, *p = out;
+ char *p = *dst;
+ char *end = p + osz;
bool is_dict = esc && *esc;
- int ret = 0;
+ int ret;

while (isz--) {
unsigned char c = *src++;
@@ -462,55 +462,33 @@ int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
(is_dict && !strchr(esc, c))) {
/* do nothing */
} else {
- if (flags & ESCAPE_SPACE) {
- ret = escape_space(c, &p, &osz);
- if (ret < 0)
- break;
- if (ret > 0)
- continue;
- }
-
- if (flags & ESCAPE_SPECIAL) {
- ret = escape_special(c, &p, &osz);
- if (ret < 0)
- break;
- if (ret > 0)
- continue;
- }
-
- if (flags & ESCAPE_NULL) {
- ret = escape_null(c, &p, &osz);
- if (ret < 0)
- break;
- if (ret > 0)
- continue;
- }
+ if (flags & ESCAPE_SPACE && escape_space(c, &p, end))
+ continue;
+
+ if (flags & ESCAPE_SPECIAL && escape_special(c, &p, end))
+ continue;
+
+ if (flags & ESCAPE_NULL && escape_null(c, &p, end))
+ continue;

/* ESCAPE_OCTAL and ESCAPE_HEX always go last */
- if (flags & ESCAPE_OCTAL) {
- ret = escape_octal(c, &p, &osz);
- if (ret < 0)
- break;
+ if (flags & ESCAPE_OCTAL && escape_octal(c, &p, end))
continue;
- }
- if (flags & ESCAPE_HEX) {
- ret = escape_hex(c, &p, &osz);
- if (ret < 0)
- break;
+
+ if (flags & ESCAPE_HEX && escape_hex(c, &p, end))
continue;
- }
}

- ret = escape_passthrough(c, &p, &osz);
- if (ret < 0)
- break;
+ escape_passthrough(c, &p, end);
}

- *dst = p;
-
- if (ret < 0)
- return ret;
+ if (p > end) {
+ *dst = end;
+ return -ENOMEM;
+ }

- return p - out;
+ ret = p - *dst;
+ *dst = p;
+ return ret;
}
EXPORT_SYMBOL(string_escape_mem);
--
2.1.3


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