Add functions for saving fd's and other values in the environment via
setenv, and for reading them back via getenv.
I understand that the rest of the series will rely on environment variables to associate and recover the child-passed FDs, but I am not really convinced that it is a good idea.
Environment variables have a number of issues that we may encounter down the road: namespace, limits, concurrency, observability etc.. I wonder if the VMState couldn't have a section about the FD to recover. Or maybe just another shared memory region?
Some comments below. These new utils could also have some unit tests.
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 c48dd37..8647a97 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2865,6 +2865,8 @@ 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);
Please use qemu prefix, that avoids potential confusion with system libraries.
+
+#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);
No check for success / truncation...
Please use g_autofree char *var = g_strdup_printf()..
+ val = getenv(var);
For consistency, I'd use g_getenv()
+ 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);
g_strdup_printf
+ setenv(var, val_str, 1);
g_setenv(), and return error value (or assert() if that makes more sense)
+}
+
+static void unsetenv_ulong(const char *prefix, const char *name)
+{
+ char var[80];
+ snprintf(var, sizeof(var), "%s%s", prefix, name);
+ unsetenv(var);
g_unsetenv
+}
+
+int getenv_fd(const char *name)
+{
+ int err;
+ int fd = getenv_ulong(FD_PREFIX, name, &err);
I'd try to use qemu_parse_fd() instead.
+ return err ? -1 : fd;
+}
+
+void setenv_fd(const char *name, int fd)
+{
Maybe check fd >= 0 ?
+ 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);
That seems to be a leftover.
+}
+
+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);
g_strndup() to avoid potential buffer overflow.
+ name[val - str] = 0;
+ if (cb(name, val + 1, handle)) {
+ return 1;
+ }
+ }
+ }
+ return 0;
+}
+
+void printenv(void)
+{
+ char **ptr = environ;
+ while (*ptr) {
+ puts(*ptr++);
+ }
+}
Is this really useful? I doubt it.
diff --git a/util/meson.build b/util/meson.build
index 0ffd7f4..5e8097a 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -23,6 +23,7 @@ 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