Hi
On Wed, Jul 7, 2021 at 9:30 PM Steve Sistare <steven.sist...@oracle.com>
wrote:
> 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.sist...@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.dovga...@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);
>
g_strdup_printf
> + 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
>
>
>
--
Marc-André Lureau
