[PATCH V4 10/25] util: env var helpers

[Steve Sistare <steven.sistare@oracle.com>]

Add functions for saving fd's and other values in the environment via
setenv, and for reading them back via getenv.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 MAINTAINERS        |  2 ++
 include/qemu/env.h | 23 +++++++++++++
 util/env.c         | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 util/meson.build   |  1 +
 4 files changed, 121 insertions(+)
 create mode 100644 include/qemu/env.h
 create mode 100644 util/env.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d4d1e9d..b844f3f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2850,6 +2850,8 @@ S: Maintained
 F: include/migration/cpr.h
 F: migration/cpr.c
 F: qapi/cpr.json
+F: include/qemu/env.h
+F: util/env.c
 
 Record/replay
 M: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
diff --git a/include/qemu/env.h b/include/qemu/env.h
new file mode 100644
index 0000000..3dad503
--- /dev/null
+++ b/include/qemu/env.h
@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2021 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_ENV_H
+#define QEMU_ENV_H
+
+#define FD_PREFIX "QEMU_FD_"
+
+typedef int (*walkenv_cb)(const char *name, const char *val, void *handle);
+
+int getenv_fd(const char *name);
+void setenv_fd(const char *name, int fd);
+void unsetenv_fd(const char *name);
+void unsetenv_fdv(const char *fmt, ...);
+int walkenv(const char *prefix, walkenv_cb cb, void *handle);
+void printenv(void);
+
+#endif
diff --git a/util/env.c b/util/env.c
new file mode 100644
index 0000000..863678d
--- /dev/null
+++ b/util/env.c
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2021 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/cutils.h"
+#include "qemu/env.h"
+
+static uint64_t getenv_ulong(const char *prefix, const char *name, int *err)
+{
+    char var[80], *val;
+    uint64_t res = 0;
+
+    snprintf(var, sizeof(var), "%s%s", prefix, name);
+    val = getenv(var);
+    if (val) {
+        *err = qemu_strtoul(val, NULL, 10, &res);
+    } else {
+        *err = -ENOENT;
+    }
+    return res;
+}
+
+static void setenv_ulong(const char *prefix, const char *name, uint64_t val)
+{
+    char var[80], val_str[80];
+    snprintf(var, sizeof(var), "%s%s", prefix, name);
+    snprintf(val_str, sizeof(val_str), "%"PRIu64, val);
+    setenv(var, val_str, 1);
+}
+
+static void unsetenv_ulong(const char *prefix, const char *name)
+{
+    char var[80];
+    snprintf(var, sizeof(var), "%s%s", prefix, name);
+    unsetenv(var);
+}
+
+int getenv_fd(const char *name)
+{
+    int err;
+    int fd = getenv_ulong(FD_PREFIX, name, &err);
+    return err ? -1 : fd;
+}
+
+void setenv_fd(const char *name, int fd)
+{
+    setenv_ulong(FD_PREFIX, name, fd);
+}
+
+void unsetenv_fd(const char *name)
+{
+    unsetenv_ulong(FD_PREFIX, name);
+}
+
+void unsetenv_fdv(const char *fmt, ...)
+{
+    va_list args;
+    char buf[80];
+    va_start(args, fmt);
+    vsnprintf(buf, sizeof(buf), fmt, args);
+    va_end(args);
+}
+
+int walkenv(const char *prefix, walkenv_cb cb, void *handle)
+{
+    char *str, name[128];
+    char **envp = environ;
+    size_t prefix_len = strlen(prefix);
+
+    while (*envp) {
+        str = *envp++;
+        if (!strncmp(str, prefix, prefix_len)) {
+            char *val = strchr(str, '=');
+            str += prefix_len;
+            strncpy(name, str, val - str);
+            name[val - str] = 0;
+            if (cb(name, val + 1, handle)) {
+                return 1;
+            }
+        }
+    }
+    return 0;
+}
+
+void printenv(void)
+{
+    char **ptr = environ;
+    while (*ptr) {
+        puts(*ptr++);
+    }
+}
diff --git a/util/meson.build b/util/meson.build
index 510765c..d2d90cc 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -22,6 +22,7 @@ util_ss.add(files('host-utils.c'))
 util_ss.add(files('bitmap.c', 'bitops.c'))
 util_ss.add(files('fifo8.c'))
 util_ss.add(files('cacheinfo.c', 'cacheflush.c'))
+util_ss.add(files('env.c'))
 util_ss.add(files('error.c', 'qemu-error.c'))
 util_ss.add(files('qemu-print.c'))
 util_ss.add(files('id.c'))
-- 
1.8.3.1