util: Introduce a parser for kernel cmdline arguments

Introduce two utility functions to parse a kernel command
line string according to the kernel code parsing rules in
order to enable the caller to perform operations such as
verifying whether certain argument=value combinations are
present or retrieving an argument's value.
Signed-off-by: NPaulo de Rezende Pinatti <ppinatti@linux.ibm.com>
Signed-off-by: NBoris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/libvirt_private.syms

@@ -3433,6 +3433,8 @@ virGetUserShell;
 virHostGetDRMRenderNode;
 virHostHasIOMMU;
 virIndexToDiskName;
+virKernelCmdlineMatchParam;
+virKernelCmdlineNextParam;
 virMemoryLimitIsSet;
 virMemoryLimitTruncate;
 virMemoryMaxValue;

src/util/virutil.c

@@ -1701,6 +1701,192 @@ virHostGetDRMRenderNode(void)
     return ret;
 }
 
+
+static const char *virKernelCmdlineSkipQuote(const char *cmdline,
+                                             bool *is_quoted)
+{
+    if (cmdline[0] == '"') {
+        *is_quoted = !(*is_quoted);
+        cmdline++;
+    }
+    return cmdline;
+}
+
+
+/**
+ * virKernelCmdlineFindEqual:
+ * @cmdline: target kernel command line string
+ * @is_quoted: indicates whether the string begins with quotes
+ * @res: pointer to the position immediately after the parsed parameter,
+ * can be used in subsequent calls to process further parameters until
+ * the end of the string.
+ *
+ * Iterate over the provided kernel command line string while honoring
+ * the kernel quoting rules and returns the index of the equal sign
+ * separating argument and value.
+ *
+ * Returns 0 for the cases where no equal sign is found or the argument
+ * itself begins with the equal sign (both cases indicating that the
+ * argument has no value). Otherwise, returns the index of the equal
+ * sign in the string.
+ */
+static size_t virKernelCmdlineFindEqual(const char *cmdline,
+                                        bool is_quoted,
+                                        const char **res)
+{
+    size_t i;
+    size_t equal_index = 0;
+
+    for (i = 0; cmdline[i]; i++) {
+        if (!(is_quoted) && g_ascii_isspace(cmdline[i]))
+            break;
+        if (equal_index == 0 && cmdline[i] == '=') {
+            equal_index = i;
+            continue;
+        }
+        virKernelCmdlineSkipQuote(cmdline + i, &is_quoted);
+    }
+    *res = cmdline + i;
+    return equal_index;
+}
+
+
+static char* virKernelArgNormalize(const char *arg)
+{
+    return virStringReplace(arg, "_", "-");
+}
+
+
+/**
+ * virKernelCmdlineNextParam:
+ * @cmdline: kernel command line string to be checked for next parameter
+ * @param: pointer to hold retrieved parameter, will be NULL if none found
+ * @val: pointer to hold retrieved value of @param
+ *
+ * Parse the kernel cmdline and store the next parameter in @param
+ * and the value of @param in @val which can be NULL if @param has
+ * no value. In addition returns the address right after @param=@value
+ * for possible further processing.
+ *
+ * Returns a pointer to address right after @param=@val in the
+ * kernel command line, will point to the string's end (NULL)
+ * in case no next parameter is found
+ */
+const char *virKernelCmdlineNextParam(const char *cmdline,
+                                      char **param,
+                                      char **val)
+{
+    const char *next;
+    int equal_index;
+    bool is_quoted = false;
+    *param = NULL;
+    *val = NULL;
+
+    virSkipSpaces(&cmdline);
+    cmdline = virKernelCmdlineSkipQuote(cmdline, &is_quoted);
+    equal_index = virKernelCmdlineFindEqual(cmdline, is_quoted, &next);
+
+    if (next == cmdline)
+        return next;
+
+    /* param has no value */
+    if (equal_index == 0) {
+        if (is_quoted && next[-1] == '"')
+            *param = g_strndup(cmdline, next - cmdline - 1);
+        else
+            *param = g_strndup(cmdline, next - cmdline);
+        return next;
+    }
+
+    *param = g_strndup(cmdline, equal_index);
+
+    if (cmdline[equal_index + 1] == '"') {
+        is_quoted = true;
+        equal_index++;
+    }
+
+    if (is_quoted && next[-1] == '"')
+        *val = g_strndup(cmdline + equal_index + 1,
+                         next - cmdline - equal_index - 2);
+    else
+        *val = g_strndup(cmdline + equal_index + 1,
+                         next - cmdline - equal_index - 1);
+    return next;
+}
+
+
+static bool virKernelCmdlineStrCmp(const char *kernel_val,
+                                   const char *caller_val,
+                                   virKernelCmdlineFlags flags)
+{
+    if (flags & VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX)
+        return STRPREFIX(kernel_val, caller_val);
+    return STREQ(kernel_val, caller_val);
+}
+
+
+/**
+ * virKernelCmdlineMatchParam:
+ * @cmdline: kernel command line string to be checked for @arg
+ * @arg: kernel command line argument
+ * @values: array of possible values to match @arg
+ * @len_values: size of array, it can be 0 meaning a match will be positive if
+ *              the argument has no value.
+ * @flags: bitwise-OR of virKernelCmdlineFlags
+ *
+ * Try to match the provided kernel cmdline string with the provided @arg
+ * and the list @values of possible values according to the matching strategy
+ * defined in @flags.
+ *
+ *
+ * Returns true if a match is found, false otherwise
+ */
+bool virKernelCmdlineMatchParam(const char *cmdline,
+                                const char *arg,
+                                const char **values,
+                                size_t len_values,
+                                virKernelCmdlineFlags flags)
+{
+    bool match = false;
+    size_t i;
+    const char *next = cmdline;
+    g_autofree char *arg_norm = virKernelArgNormalize(arg);
+
+    while (next[0] != '\0') {
+        g_autofree char *kparam = NULL;
+        g_autofree char *kparam_norm = NULL;
+        g_autofree char *kval = NULL;
+
+        next = virKernelCmdlineNextParam(next, &kparam, &kval);
+
+        if (!kparam)
+            break;
+
+        kparam_norm = virKernelArgNormalize(kparam);
+
+        if (STRNEQ(kparam_norm, arg_norm))
+            continue;
+
+        if (!kval) {
+            match = (len_values == 0) ? true : false;
+        } else {
+            match = false;
+            for (i = 0; i < len_values; i++) {
+                if (virKernelCmdlineStrCmp(kval, values[i], flags)) {
+                    match = true;
+                    break;
+                }
+            }
+        }
+
+        if (match && (flags & VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST))
+            break;
+    }
+
+    return match;
+}
+
+
 /*
  * Get a password from the console input stream.
  * The caller must free the returned password.

src/util/virutil.h

@@ -145,6 +145,40 @@ bool virHostHasIOMMU(void);
 
 char *virHostGetDRMRenderNode(void) G_GNUC_NO_INLINE;
 
+/* Kernel cmdline match and comparison strategy for arg=value pairs */
+typedef enum {
+    /* substring comparison of argument values */
+    VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX = 1,
+
+    /* strict string comparison of argument values */
+    VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ = 2,
+
+    /* look for any occurrence of the argument with the expected value,
+     * this should be used when an argument set to the expected value overrides
+     * all the other occurrences of the argument, e.g. when looking for 'arg=1'
+     * in 'arg=0 arg=1 arg=0' the search would succeed with this flag
+     */
+    VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST = 4,
+
+    /* look for the last occurrence of argument with the expected value,
+     * this should be used when the last occurrence of the argument overrides
+     * all the other ones, e.g. when looking for 'arg=1' in 'arg=0 arg=1' the
+     * search would succeed with this flag, but in 'arg=1 arg=0' it would not,
+     * because 'arg=0' overrides all the previous occurrences of 'arg'
+     */
+    VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST = 8,
+} virKernelCmdlineFlags;
+
+const char *virKernelCmdlineNextParam(const char *cmdline,
+                                      char **param,
+                                      char **val);
+
+bool virKernelCmdlineMatchParam(const char *cmdline,
+                                const char *arg,
+                                const char **values,
+                                size_t len_values,
+                                virKernelCmdlineFlags flags);
+
 /**
  * VIR_ASSIGN_IS_OVERFLOW:
  * @rvalue: value that is checked (evaluated twice)

tests/utiltest.c

@@ -254,6 +254,140 @@ testOverflowCheckMacro(const void *data G_GNUC_UNUSED)
 }
 
 
+struct testKernelCmdlineNextParamData
+{
+    const char *cmdline;
+    const char *param;
+    const char *val;
+    const char *next;
+};
+
+static struct testKernelCmdlineNextParamData kEntries[] = {
+    { "arg1 arg2 arg3=val1",                        "arg1",              NULL,                  " arg2 arg3=val1"      },
+    { "arg1=val1 arg2 arg3=val3 arg4",              "arg1",              "val1",                " arg2 arg3=val3 arg4" },
+    { "arg1=sub1=val1,sub2=val2 arg3=val3 arg4",    "arg1",              "sub1=val1,sub2=val2", " arg3=val3 arg4"      },
+    { "arg3=val3 ",                                 "arg3",              "val3",                " "                    },
+    { "arg3=val3",                                  "arg3",              "val3",                ""                     },
+    { "arg-3=val3 arg4",                            "arg-3",             "val3",                " arg4"                },
+    { " arg_3=val3 arg4",                           "arg_3",             "val3",                " arg4"                },
+    { "arg2=\"value with space\" arg3=val3",        "arg2",              "value with space",    " arg3=val3"           },
+    { " arg2=\"value with space\"   arg3=val3",     "arg2",              "value with space",    "   arg3=val3"         },
+    { "  \"arg2=value with space\" arg3=val3",      "arg2",              "value with space",    " arg3=val3"           },
+    { "arg2=\"val\"ue arg3",                        "arg2",              "val\"ue",             " arg3"                },
+    { "arg2=value\" long\" arg3",                   "arg2",              "value\" long\"",      " arg3"                },
+    { " \"arg2 with space=value with space\" arg3", "arg2 with space",   "value with space",    " arg3"                },
+    { " arg2\" with space=val2\" arg3",             "arg2\" with space", "val2\"",              " arg3"                },
+    { " arg2longer=someval\" long\" arg2=val2",     "arg2longer",        "someval\" long\"",    " arg2=val2"           },
+    { "=val1 arg2=val2",                            "=val1",             NULL,                  " arg2=val2"           },
+    { " ",                                          NULL,                NULL,                  ""                     },
+    { "",                                           NULL,                NULL,                  ""                     },
+};
+
+static int
+testKernelCmdlineNextParam(const void *data G_GNUC_UNUSED)
+{
+    const char *next;
+    size_t i;
+
+    for (i = 0; i < G_N_ELEMENTS(kEntries); ++i) {
+        g_autofree char * param = NULL;
+        g_autofree char * val = NULL;
+
+        next = virKernelCmdlineNextParam(kEntries[i].cmdline, &param, &val);
+
+        if (STRNEQ_NULLABLE(param, kEntries[i].param) ||
+            STRNEQ_NULLABLE(val, kEntries[i].val) ||
+            STRNEQ(next, kEntries[i].next)) {
+            VIR_TEST_DEBUG("\nKernel cmdline [%s]", kEntries[i].cmdline);
+            VIR_TEST_DEBUG("Expect param [%s]", kEntries[i].param);
+            VIR_TEST_DEBUG("Actual param [%s]", param);
+            VIR_TEST_DEBUG("Expect value [%s]", kEntries[i].val);
+            VIR_TEST_DEBUG("Actual value [%s]", val);
+            VIR_TEST_DEBUG("Expect next [%s]", kEntries[i].next);
+            VIR_TEST_DEBUG("Actual next [%s]", next);
+
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+
+struct testKernelCmdlineMatchData
+{
+    const char *cmdline;
+    const char *arg;
+    const char *values[2];
+    virKernelCmdlineFlags flags;
+    bool result;
+};
+
+static struct testKernelCmdlineMatchData kMatchEntries[] = {
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"1", "y"},          VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,     false },
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"on", "yes"},       VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,     true  },
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"1", "y"},          VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST | VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX, true  },
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"a", "b"},          VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST | VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX, false },
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"on", "yes"},       VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,      false },
+    {"arg1 myarg=no arg2=val2 myarg=yes arg4=val4 myarg=no arg5", "myarg",  {"1", "y"},          VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX,  false },
+    {"arg1 myarg=no arg2=val2 arg4=val4 myarg=yes arg5",          "myarg",  {"on", "yes"},       VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,      true  },
+    {"arg1 myarg=no arg2=val2 arg4=val4 myarg=yes arg5",          "myarg",  {"1", "y"},          VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX,  true  },
+    {"arg1 myarg=no arg2=val2 arg4=val4 myarg arg5",              "myarg",  {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        true  },
+    {"arg1 myarg arg2=val2 arg4=val4 myarg=yes arg5",             "myarg",  {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST,                                       true  },
+    {"arg1 myarg arg2=val2 arg4=val4 myarg=yes arg5",             "myarg",  {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        false },
+    {"arg1 my-arg=no arg2=val2 arg4=val4 my_arg=yes arg5",        "my-arg", {"on", "yes"},       VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        true  },
+    {"arg1 my-arg=no arg2=val2 arg4=val4 my_arg=yes arg5 ",       "my-arg", {"on", "yes"},       VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,      true  },
+    {"arg1 my-arg arg2=val2 arg4=val4 my_arg=yes arg5",           "my_arg", {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST,                                       true  },
+    {"arg1 my-arg arg2=val2 arg4=val4 my-arg=yes arg5",           "my_arg", {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST,                                       true  },
+    {"=arg1 my-arg arg2=val2 arg4=val4 my-arg=yes arg5",          "my_arg", {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST,                                       true  },
+    {"my-arg =arg1 arg2=val2 arg4=val4 my-arg=yes arg5",          "=arg1",  {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        true  },
+    {"arg1 arg2=val2 myarg=sub1=val1 arg5",                       "myarg",  {"sub1=val1", NULL}, VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        true  },
+    {"arg1 arg2=",                                                "arg2",   {"", ""},            VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST | VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ,      true  },
+    {" ",                                                         "myarg",  {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        false },
+    {"",                                                          "",       {NULL, NULL},        VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST,                                        false },
+};
+
+
+static int
+testKernelCmdlineMatchParam(const void *data G_GNUC_UNUSED)
+{
+    bool result;
+    size_t i, lenValues;
+
+    for (i = 0; i < G_N_ELEMENTS(kMatchEntries); ++i) {
+        if (kMatchEntries[i].values[0] == NULL)
+            lenValues = 0;
+        else
+            lenValues = G_N_ELEMENTS(kMatchEntries[i].values);
+
+        result = virKernelCmdlineMatchParam(kMatchEntries[i].cmdline,
+                                            kMatchEntries[i].arg,
+                                            kMatchEntries[i].values,
+                                            lenValues,
+                                            kMatchEntries[i].flags);
+
+        if (result != kMatchEntries[i].result) {
+            VIR_TEST_DEBUG("\nKernel cmdline [%s]", kMatchEntries[i].cmdline);
+            VIR_TEST_DEBUG("Kernel argument [%s]", kMatchEntries[i].arg);
+            VIR_TEST_DEBUG("Kernel values [%s] [%s]", kMatchEntries[i].values[0],
+                           kMatchEntries[i].values[1]);
+            if (kMatchEntries[i].flags & VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX)
+                VIR_TEST_DEBUG("Flag [VIR_KERNEL_CMDLINE_FLAGS_CMP_PREFIX]");
+            if (kMatchEntries[i].flags & VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ)
+                VIR_TEST_DEBUG("Flag [VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ]");
+            if (kMatchEntries[i].flags & VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST)
+                VIR_TEST_DEBUG("Flag [VIR_KERNEL_CMDLINE_FLAGS_SEARCH_FIRST]");
+            if (kMatchEntries[i].flags & VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST)
+                VIR_TEST_DEBUG("Flag [VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST]");
+            VIR_TEST_DEBUG("Expect result [%d]", kMatchEntries[i].result);
+            VIR_TEST_DEBUG("Actual result [%d]", result);
+
+            return -1;
+        }
+    }
+
+    return 0;
+}
 
 
 static int
@@ -277,6 +411,8 @@ mymain(void)
     DO_TEST(ParseVersionString);
     DO_TEST(RoundValueToPowerOfTwo);
     DO_TEST(OverflowCheckMacro);
+    DO_TEST(KernelCmdlineNextParam);
+    DO_TEST(KernelCmdlineMatchParam);
 
     return result == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }