Re: [Qemu-devel] [PATCH v2 1/8] util: Add UUID API

[Markus Armbruster <armbru@redhat.com>]

Fam Zheng <famz@redhat.com> writes:

> A number of different places across the code base use CONFIG_UUID. Some
> of them are soft dependency, some are not built if libuuid is not
> available, some come with dummy fallback, some throws runtime error.
>
> It is hard to maintain, and hard to reason for users.
>
> Since UUID is a simple standard with only a small number of operations,
> it is cleaner to have a central support in libqemuutil. This patch adds
> qemu_uuid_* the functions so that all uuid users in the code base can
> rely on. Except for qemu_uuid_generate which is new code, all other
> functions are just copy from existing fallbacks from other files.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  arch_init.c             | 19 --------------
>  block/iscsi.c           |  2 +-
>  hw/smbios/smbios.c      |  1 +
>  include/qemu/uuid.h     | 40 +++++++++++++++++++++++++++++
>  include/sysemu/sysemu.h |  4 ---
>  qmp.c                   |  1 +
>  stubs/uuid.c            |  2 +-
>  util/Makefile.objs      |  1 +
>  util/uuid.c             | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
>  vl.c                    |  1 +
>  10 files changed, 114 insertions(+), 25 deletions(-)
>  create mode 100644 include/qemu/uuid.h
>  create mode 100644 util/uuid.c
>
> diff --git a/arch_init.c b/arch_init.c
> index fa05973..5cc58b2 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -235,25 +235,6 @@ void audio_init(void)
>      }
>  }
>  
> -int qemu_uuid_parse(const char *str, uint8_t *uuid)
> -{
> -    int ret;
> -
> -    if (strlen(str) != 36) {
> -        return -1;
> -    }
> -
> -    ret = sscanf(str, UUID_FMT, &uuid[0], &uuid[1], &uuid[2], &uuid[3],
> -                 &uuid[4], &uuid[5], &uuid[6], &uuid[7], &uuid[8], &uuid[9],
> -                 &uuid[10], &uuid[11], &uuid[12], &uuid[13], &uuid[14],
> -                 &uuid[15]);
> -
> -    if (ret != 16) {
> -        return -1;
> -    }
> -    return 0;
> -}
> -
>  void do_acpitable_option(const QemuOpts *opts)
>  {
>  #ifdef TARGET_I386
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 95ce9e1..961ac76 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -36,7 +36,7 @@
>  #include "block/block_int.h"
>  #include "block/scsi.h"
>  #include "qemu/iov.h"
> -#include "sysemu/sysemu.h"
> +#include "qemu/uuid.h"
>  #include "qmp-commands.h"
>  #include "qapi/qmp/qstring.h"
>  #include "crypto/secret.h"
> diff --git a/hw/smbios/smbios.c b/hw/smbios/smbios.c
> index 74c7102..0705eb1 100644
> --- a/hw/smbios/smbios.c
> +++ b/hw/smbios/smbios.c
> @@ -20,6 +20,7 @@
>  #include "qemu/config-file.h"
>  #include "qemu/error-report.h"
>  #include "sysemu/sysemu.h"
> +#include "qemu/uuid.h"
>  #include "sysemu/cpus.h"
>  #include "hw/smbios/smbios.h"
>  #include "hw/loader.h"
> diff --git a/include/qemu/uuid.h b/include/qemu/uuid.h
> new file mode 100644
> index 0000000..854a208
> --- /dev/null
> +++ b/include/qemu/uuid.h
> @@ -0,0 +1,40 @@
> +/*
> + *  QEMU UUID functions
> + *
> + *  Copyright 2016 Red Hat, Inc.,
> + *
> + *  Authors:
> + *   Fam Zheng <famz@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the Free
> + * Software Foundation; either version 2 of the License, or (at your option)
> + * any later version.
> + *
> + */
> +
> +#ifndef QEMU_UUID_H
> +#define QEMU_UUID_H
> +
> +#include "qemu-common.h"
> +
> +typedef unsigned char QemuUUID[16];

I'm afraid this typedef is problematic.  Consider:

    void use_uuid(QemuUUID uuid)
    {
        printf("sizeof(uuid) %zd\n", sizeof(uuid));
        uuid[0]++;
    }

QemuUUID is obviously a typedef name, so a reasonable reader may assume
(1) sizeof(uuid) is the size of the uuid, and (2) since uuid is passed
by value, the increment is not visible outside the function.  Both
assumptions are wrong, because array arguments degenerate into pointers.

I recommend to wrap it in a struct.

> +
> +#define UUID_FMT "%02hhx%02hhx%02hhx%02hhx-" \
> +                 "%02hhx%02hhx-%02hhx%02hhx-" \
> +                 "%02hhx%02hhx-" \
> +                 "%02hhx%02hhx%02hhx%02hhx%02hhx%02hhx"
> +
> +#define UUID_FMT_LEN 36
> +
> +#define UUID_NONE "00000000-0000-0000-0000-000000000000"
> +
> +void qemu_uuid_generate(QemuUUID out);
> +
> +int qemu_uuid_is_null(const QemuUUID uu);
> +
> +void qemu_uuid_unparse(const QemuUUID uu, char *out);
> +
> +int qemu_uuid_parse(const char *str, uint8_t *uuid);
> +
> +#endif
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index ee7c760..6111950 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -18,10 +18,6 @@ extern const char *bios_name;
>  extern const char *qemu_name;
>  extern uint8_t qemu_uuid[];
>  extern bool qemu_uuid_set;
> -int qemu_uuid_parse(const char *str, uint8_t *uuid);
> -
> -#define UUID_FMT "%02hhx%02hhx%02hhx%02hhx-%02hhx%02hhx-%02hhx%02hhx-%02hhx%02hhx-%02hhx%02hhx%02hhx%02hhx%02hhx%02hhx"
> -#define UUID_NONE "00000000-0000-0000-0000-000000000000"
>  
>  bool runstate_check(RunState state);
>  void runstate_set(RunState new_state);
> diff --git a/qmp.c b/qmp.c
> index b6d531e..7fbde29 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -35,6 +35,7 @@
>  #include "qom/object_interfaces.h"
>  #include "hw/mem/pc-dimm.h"
>  #include "hw/acpi/acpi_dev_interface.h"
> +#include "qemu/uuid.h"
>  
>  NameInfo *qmp_query_name(Error **errp)
>  {
> diff --git a/stubs/uuid.c b/stubs/uuid.c
> index 92ad717..a880de8 100644
> --- a/stubs/uuid.c
> +++ b/stubs/uuid.c
> @@ -1,6 +1,6 @@
>  #include "qemu/osdep.h"
>  #include "qemu-common.h"
> -#include "sysemu/sysemu.h"
> +#include "qemu/uuid.h"
>  #include "qmp-commands.h"
>  
>  UuidInfo *qmp_query_uuid(Error **errp)
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index 96cb1e0..31bba15 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -20,6 +20,7 @@ util-obj-y += iov.o qemu-config.o qemu-sockets.o uri.o notify.o
>  util-obj-y += qemu-option.o qemu-progress.o
>  util-obj-y += hexdump.o
>  util-obj-y += crc32c.o
> +util-obj-y += uuid.o
>  util-obj-y += throttle.o
>  util-obj-y += getauxval.o
>  util-obj-y += readline.o
> diff --git a/util/uuid.c b/util/uuid.c
> new file mode 100644
> index 0000000..9e26560
> --- /dev/null
> +++ b/util/uuid.c
> @@ -0,0 +1,68 @@
> +/*
> + *  QEMU UUID functions
> + *
> + *  Copyright 2016 Red Hat, Inc.,
> + *
> + *  Authors:
> + *   Fam Zheng <famz@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the Free
> + * Software Foundation; either version 2 of the License, or (at your option)
> + * any later version.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu-common.h"
> +#include "qemu/uuid.h"
> +#include <glib.h>
> +
> +void qemu_uuid_generate(QemuUUID out)
> +{
> +    /* Version 4 UUID, RFC4122 4.4. */
> +    QEMU_BUILD_BUG_ON(sizeof(QemuUUID) != 16);
> +    *((guint32 *)out + 0) = g_random_int();
> +    *((guint32 *)out + 1) = g_random_int();
> +    *((guint32 *)out + 2) = g_random_int();
> +    *((guint32 *)out + 3) = g_random_int();

I loathe GLib's pointless duplication of the standard integer types.
Sure we can't simply use uint32_t?

Possibly:

    uint32_t *out32 = (uint32_t)out;
    out32[0] = g_random_int();
    out32[1] = g_random_int();
    out32[2] = g_random_int();
    out32[3] = g_random_int();

> +    /* Set the two most significant bits (bits 6 and 7) of the
> +      clock_seq_hi_and_reserved to zero and one, respectively. */
> +    out[8] = (out[8] & 0x3f) | 0x80;
> +    /* Set the four most significant bits (bits 12 through 15) of the
> +      time_hi_and_version field to the 4-bit version number.
> +      */
> +    out[6] = (out[6] & 0xf) | 0x40;
> +}
> +
> +int qemu_uuid_is_null(const QemuUUID uu)
> +{
> +    QemuUUID null_uuid = { 0 };
> +    return memcmp(uu, null_uuid, sizeof(QemuUUID)) == 0;
> +}
> +
> +void qemu_uuid_unparse(const QemuUUID uu, char *out)

While there, you could write a function contract that spells out that
@out[] must have space for 37 characters.

> +{
> +    snprintf(out, 37, UUID_FMT,
> +             uu[0], uu[1], uu[2], uu[3], uu[4], uu[5], uu[6], uu[7],
> +             uu[8], uu[9], uu[10], uu[11], uu[12], uu[13], uu[14], uu[15]);
> +}
> +
> +int qemu_uuid_parse(const char *str, uint8_t *uuid)
> +{
> +    int ret;
> +
> +    if (strlen(str) != 36) {
> +        return -1;
> +    }
> +
> +    ret = sscanf(str, UUID_FMT, &uuid[0], &uuid[1], &uuid[2], &uuid[3],
> +                 &uuid[4], &uuid[5], &uuid[6], &uuid[7], &uuid[8], &uuid[9],
> +                 &uuid[10], &uuid[11], &uuid[12], &uuid[13], &uuid[14],
> +                 &uuid[15]);
> +
> +    if (ret != 16) {
> +        return -1;
> +    }
> +    return 0;
> +}
> diff --git a/vl.c b/vl.c
> index e7c2c62..8b12f34 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -25,6 +25,7 @@
>  #include "qemu-version.h"
>  #include "qemu/cutils.h"
>  #include "qemu/help_option.h"
> +#include "qemu/uuid.h"
>  
>  #ifdef CONFIG_SECCOMP
>  #include "sysemu/seccomp.h"