[Qemu-devel] [PATCH] linux-user: Add generic env variable handling

[Riku Voipio <riku.voipio@iki.fi>]

Adds support for qemu to modify target process environment
variables using -E and -U commandline switches. This replaces
eventually the -drop-ld-preload flag.

From: Mika Westerberg

Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
---
 Makefile.target      |    2 +-
 linux-user/envlist.c |  247 ++++++++++++++++++++++++++++++++++++++++++++++++++
 linux-user/envlist.h |   22 +++++
 linux-user/main.c    |   50 +++++++---
 4 files changed, 304 insertions(+), 17 deletions(-)
 create mode 100644 linux-user/envlist.c
 create mode 100644 linux-user/envlist.h

diff --git a/Makefile.target b/Makefile.target
index fcaf4ec..a736343 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -373,7 +373,7 @@ CFLAGS+=-p
 endif
 
 OBJS= main.o syscall.o strace.o mmap.o signal.o path.o thunk.o \
-      elfload.o linuxload.o uaccess.o
+      elfload.o linuxload.o uaccess.o envlist.o
 LIBS+= $(AIOLIBS)
 ifdef TARGET_HAS_BFLT
 OBJS+= flatload.o
diff --git a/linux-user/envlist.c b/linux-user/envlist.c
new file mode 100644
index 0000000..e13c2d3
--- /dev/null
+++ b/linux-user/envlist.c
@@ -0,0 +1,247 @@
+#include <sys/queue.h>
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "envlist.h"
+
+struct envlist_entry {
+	const char *ev_var;			/* actual env value */
+	LIST_ENTRY(envlist_entry) ev_link;
+};
+
+struct envlist {
+	LIST_HEAD(, envlist_entry) el_entries;	/* actual entries */
+	size_t el_count;			/* number of entries */
+};
+
+static int envlist_parse(envlist_t *envlist,
+    const char *env, int (*)(envlist_t *, const char *));
+
+/*
+ * Allocates new envlist and returns pointer to that or
+ * NULL in case of error.
+ */
+envlist_t *
+envlist_create(void)
+{
+	envlist_t *envlist;
+
+	if ((envlist = malloc(sizeof (*envlist))) == NULL)
+		return (NULL);
+
+	LIST_INIT(&envlist->el_entries);
+	envlist->el_count = 0;
+
+	return (envlist);
+}
+
+/*
+ * Releases given envlist and its entries.
+ */
+void
+envlist_free(envlist_t *envlist)
+{
+	struct envlist_entry *entry;
+
+	assert(envlist != NULL);
+
+	while (envlist->el_entries.lh_first != NULL) {
+		entry = envlist->el_entries.lh_first;
+		LIST_REMOVE(entry, ev_link);
+
+		free((char *)entry->ev_var);
+		free(entry);
+	}
+	free(envlist);
+}
+
+/*
+ * Parses comma separated list of set/modify environment
+ * variable entries and updates given enlist accordingly.
+ *
+ * For example:
+ *     envlist_parse(el, "HOME=foo,SHELL=/bin/sh");
+ *
+ * inserts/sets environment variables HOME and SHELL.
+ *
+ * Returns 0 on success, errno otherwise.
+ */
+int
+envlist_parse_set(envlist_t *envlist, const char *env)
+{
+	return (envlist_parse(envlist, env, &envlist_setenv));
+}
+
+/*
+ * Parses comma separated list of unset environment variable
+ * entries and removes given variables from given envlist.
+ *
+ * Returns 0 on success, errno otherwise.
+ */
+int
+envlist_parse_unset(envlist_t *envlist, const char *env)
+{
+	return (envlist_parse(envlist, env, &envlist_unsetenv));
+}
+
+/*
+ * Parses comma separated list of set, modify or unset entries
+ * and calls given callback for each entry.
+ *
+ * Returns 0 in case of success, errno otherwise.
+ */
+static int
+envlist_parse(envlist_t *envlist, const char *env,
+    int (*callback)(envlist_t *, const char *))
+{
+	char *tmpenv, *envvar;
+	char *envsave = NULL;
+
+	assert(callback != NULL);
+
+	if ((envlist == NULL) || (env == NULL))
+		return (EINVAL);
+
+	/*
+	 * We need to make temporary copy of the env string
+	 * as strtok_r(3) modifies it while it tokenizes.
+	 */
+	if ((tmpenv = strdup(env)) == NULL)
+		return (errno);
+
+	envvar = strtok_r(tmpenv, ",", &envsave);
+	while (envvar != NULL) {
+		if ((*callback)(envlist, envvar) != 0) {
+			free(tmpenv);
+			return (errno);
+		}
+		envvar = strtok_r(NULL, ",", &envsave);
+	}
+
+	free(tmpenv);
+	return (0);
+}
+
+/*
+ * Sets environment value to envlist in similar manner
+ * than putenv(3).
+ *
+ * Returns 0 in success, errno otherwise.
+ */
+int
+envlist_setenv(envlist_t *envlist, const char *env)
+{
+	struct envlist_entry *entry = NULL;
+	const char *eq_sign;
+	size_t envname_len;
+
+	if ((envlist == NULL) || (env == NULL))
+		return (EINVAL);
+
+	/* find out first equals sign in given env */
+	if ((eq_sign = strchr(env, '=')) == NULL)
+		return (EINVAL);
+	envname_len = eq_sign - env + 1;
+
+	/*
+	 * If there already exists variable with given name
+	 * we remove and release it before allocating a whole
+	 * new entry.
+	 */
+	for (entry = envlist->el_entries.lh_first; entry != NULL;
+	    entry = entry->ev_link.le_next) {
+		if (strncmp(entry->ev_var, env, envname_len) == 0)
+			break;
+	}
+
+	if (entry != NULL) {
+		LIST_REMOVE(entry, ev_link);
+		free((char *)entry->ev_var);
+		free(entry);
+	} else {
+		envlist->el_count++;
+	}
+
+	if ((entry = malloc(sizeof (*entry))) == NULL)
+		return (errno);
+	if ((entry->ev_var = strdup(env)) == NULL) {
+		free(entry);
+		return (errno);
+	}
+	LIST_INSERT_HEAD(&envlist->el_entries, entry, ev_link);
+
+	return (0);
+}
+
+/*
+ * Removes given env value from envlist in similar manner
+ * than unsetenv(3).  Returns 0 in success, errno otherwise.
+ */
+int
+envlist_unsetenv(envlist_t *envlist, const char *env)
+{
+	struct envlist_entry *entry;
+	size_t envname_len;
+
+	if ((envlist == NULL) || (env == NULL))
+		return (EINVAL);
+
+	/* env is not allowed to contain '=' */
+	if (strchr(env, '=') != NULL)
+		return (EINVAL);
+
+	/*
+	 * Find out the requested entry and remove
+	 * it from the list.
+	 */
+	envname_len = strlen(env);
+	for (entry = envlist->el_entries.lh_first; entry != NULL;
+	    entry = entry->ev_link.le_next) {
+		if (strncmp(entry->ev_var, env, envname_len) == 0)
+			break;
+	}
+	if (entry != NULL) {
+		LIST_REMOVE(entry, ev_link);
+		free((char *)entry->ev_var);
+		free(entry);
+
+		envlist->el_count--;
+	}
+	return (0);
+}
+
+/*
+ * Returns given envlist as array of strings (in same form that
+ * global variable environ is).  Caller must free returned memory
+ * by calling free(3) for each element and for the array.  Returned
+ * array and given envlist are not related (no common references).
+ *
+ * If caller provides count pointer, number of items in array is
+ * stored there.  In case of error, NULL is returned and no memory
+ * is allocated.
+ */
+char **
+envlist_to_environ(const envlist_t *envlist, size_t *count)
+{
+	struct envlist_entry *entry;
+	char **env, **penv;
+
+	penv = env = malloc((envlist->el_count + 1) * sizeof (char *));
+	if (env == NULL)
+		return (NULL);
+
+	for (entry = envlist->el_entries.lh_first; entry != NULL;
+	    entry = entry->ev_link.le_next) {
+		*(penv++) = strdup(entry->ev_var);
+	}
+	*penv = NULL; /* NULL terminate the list */
+
+	if (count != NULL)
+		*count = envlist->el_count;
+
+	return (env);
+}
diff --git a/linux-user/envlist.h b/linux-user/envlist.h
new file mode 100644
index 0000000..e76d4a1
--- /dev/null
+++ b/linux-user/envlist.h
@@ -0,0 +1,22 @@
+#ifndef ENVLIST_H
+#define ENVLIST_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct envlist envlist_t;
+
+extern	envlist_t *envlist_create(void);
+extern	void envlist_free(envlist_t *);
+extern	int envlist_setenv(envlist_t *, const char *);
+extern	int envlist_unsetenv(envlist_t *, const char *);
+extern	int envlist_parse_set(envlist_t *, const char *);
+extern	int envlist_parse_unset(envlist_t *, const char *);
+extern	char **envlist_to_environ(const envlist_t *, size_t *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ENVLIST_H */
diff --git a/linux-user/main.c b/linux-user/main.c
index 2ffe244..21a0626 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -32,6 +32,9 @@
 /* For tb_lock */
 #include "exec-all.h"
 
+
+#include "envlist.h"
+
 #define DEBUG_LOGFILE "/tmp/qemu.log"
 
 char *exec_path;
@@ -2190,6 +2193,8 @@ static void usage(void)
            "-s size           set the stack size in bytes (default=%ld)\n"
            "-cpu model        select CPU (-cpu ? for list)\n"
            "-drop-ld-preload  drop LD_PRELOAD for target process\n"
+           "-E var=value      sets/modifies targets environment variable(s)\n"
+           "-U var            unsets targets environment variable(s)\n"
            "\n"
            "Debug options:\n"
            "-d options   activate log (logfile=%s)\n"
@@ -2199,6 +2204,12 @@ static void usage(void)
            "Environment variables:\n"
            "QEMU_STRACE       Print system calls and arguments similar to the\n"
            "                  'strace' program.  Enable by setting to any value.\n"
+           "You can use -E and -U options to set/unset environment variables\n"
+           "for target process.  It is possible to provide several variables\n"
+           "by repeating the option.  For example:\n"
+           "    -E var1=val2 -E var2=val2 -U LD_PRELOAD -U LD_DEBUG\n"
+           "Note that if you provide several changes to single variable\n"
+           "last change will stay in effect.\n"
            ,
            TARGET_ARCH,
            interp_prefix,
@@ -2233,8 +2244,8 @@ int main(int argc, char **argv, char **envp)
     int optind;
     const char *r;
     int gdbstub_port = 0;
-    int drop_ld_preload = 0, environ_count = 0;
-    char **target_environ, **wrk, **dst;
+    char **target_environ, **wrk;
+    envlist_t *envlist = NULL;
 
     if (argc <= 1)
         usage();
@@ -2244,6 +2255,16 @@ int main(int argc, char **argv, char **envp)
     /* init debug */
     cpu_set_log_filename(DEBUG_LOGFILE);
 
+    if ((envlist = envlist_create()) == NULL) {
+        (void) fprintf(stderr, "Unable to allocate envlist\n");
+        exit(1);
+    }
+
+    /* add current environment into the list */
+    for (wrk = environ; *wrk != NULL; wrk++) {
+        (void) envlist_setenv(envlist, *wrk);
+    }
+
     cpu_model = NULL;
     optind = 1;
     for(;;) {
@@ -2273,6 +2294,14 @@ int main(int argc, char **argv, char **envp)
                 _exit(1);
             }
             cpu_set_log(mask);
+        } else if (!strcmp(r, "E")) {
+            r = argv[optind++];
+            if (envlist_setenv(envlist, r) != 0)
+                usage();
+        } else if (!strcmp(r, "U")) {
+            r = argv[optind++];
+            if (envlist_unsetenv(envlist, r) != 0)
+                usage();
         } else if (!strcmp(r, "s")) {
             r = argv[optind++];
             x86_stack_size = strtol(r, (char **)&r, 0);
@@ -2305,7 +2334,7 @@ int main(int argc, char **argv, char **envp)
                 _exit(1);
             }
         } else if (!strcmp(r, "drop-ld-preload")) {
-            drop_ld_preload = 1;
+           (void) envlist_unsetenv(envlist, "LD_PRELOAD");
         } else if (!strcmp(r, "strace")) {
             do_strace = 1;
         } else
@@ -2374,19 +2403,8 @@ int main(int argc, char **argv, char **envp)
         do_strace = 1;
     }
 
-    wrk = environ;
-    while (*(wrk++))
-        environ_count++;
-
-    target_environ = malloc((environ_count + 1) * sizeof(char *));
-    if (!target_environ)
-        abort();
-    for (wrk = environ, dst = target_environ; *wrk; wrk++) {
-        if (drop_ld_preload && !strncmp(*wrk, "LD_PRELOAD=", 11))
-            continue;
-        *(dst++) = strdup(*wrk);
-    }
-    *dst = NULL; /* NULL terminate target_environ */
+    target_environ = envlist_to_environ(envlist, NULL);
+    envlist_free(envlist);
 
     if (loader_exec(filename, argv+optind, target_environ, regs, info) != 0) {
         printf("Error loading %s\n", filename);
-- 
1.5.6.5


-- 
"rm -rf" only sounds scary if you don't have backups