Hi

On Wed, Jul 7, 2021 at 9:30 PM Steve Sistare <steven.sistare@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.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);
>

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