Re: [PATCH v2 2/3] qga: add implementation of guest-get-disks for Linux

[Tomáš Golembiovský]

On Tue, Sep 29, 2020 at 07:22:00PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Mon, Sep 7, 2020 at 1:17 PM Tomáš Golembiovský <tgolembi@redhat.com>
> wrote:
> 
> > The command lists all disks (real and virtual) as well as disk
> > partitions. For each disk the list of slave disks is also listed and
> > /dev path is used as a handle so it can be matched with "name" filed of
> >
> 
> field
> 
> other returned disk entries. For disk partitions the "slave" list is
> > populated with the the parent device for easier tracking of hierarchy.
> >
> > Example output:
> > {
> >   "return": [
> >     ...
> >     {
> >       "name": "/dev/dm-0",
> >       "partition": false,
> >       "slaves": [
> >         "/dev/sda2"
> >       ],
> >       "alias": "luks-7062202e-5b9b-433e-81e8-6628c40da9f7"
> >     },
> >     {
> >       "name": "/dev/sda2",
> >       "partition": true,
> >       "slaves": [
> >         "/dev/sda"
> >       ]
> >     },
> >     {
> >       "name": "/dev/sda",
> >       "partition": false,
> >       "address": {
> >         "serial": "SAMSUNG_MZ7LN512HCHP-000L1_S1ZKNXAG822493",
> >         "bus-type": "sata",
> >         ...
> >         "dev": "/dev/sda",
> >         "target": 0
> >       },
> >       "slaves": []
> >     },
> >     ...
> >   ]
> > }
> >
> > Signed-off-by: Tomáš Golembiovský <tgolembi@redhat.com>
> > ---
> >  qga/commands-posix.c | 247 +++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 240 insertions(+), 7 deletions(-)
> >
> > diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> > index f99731af51..3babc25c09 100644
> > --- a/qga/commands-posix.c
> > +++ b/qga/commands-posix.c
> > @@ -62,6 +62,9 @@ extern char **environ;
> >  #endif
> >  #endif
> >
> > +G_DEFINE_AUTOPTR_CLEANUP_FUNC(GuestFilesystemInfo,
> > +    qapi_free_GuestFilesystemInfo)
> > +
> >
> 
> This will now conflict with qapi-gen generated headers.
> 
>  static void ga_wait_child(pid_t pid, int *status, Error **errp)
> >  {
> >      pid_t rpid;
> > @@ -1150,6 +1153,21 @@ static void
> > build_guest_fsinfo_for_virtual_device(char const *syspath,
> >      closedir(dir);
> >  }
> >
> > +static bool is_disk_virtual(const char *devpath, Error **errp)
> > +{
> > +    g_autofree char *syspath = realpath(devpath, NULL);
> > +
> > +    if (!syspath) {
> > +        error_setg_errno(errp, errno, "realpath(\"%s\")", devpath);
> >
> +        return false;
> > +    }
> > +    if (strstr(syspath, "/devices/virtual/block/")) {
> > +        return true;
> > +    } else {
> > +        return false;
> > +    }
> >
> 
>  simply to "return strstr(syspath, "/devices/virtual/block/") != NULL;" ?
> (Or strstr(syspath, "/devices/virtual/block/") ? true : false )
> 
> +}
> > +
> >  /* Dispatch to functions for virtual/real device */
> >  static void build_guest_fsinfo_for_device(char const *devpath,
> >                                            GuestFilesystemInfo *fs,
> > @@ -1168,6 +1186,7 @@ static void build_guest_fsinfo_for_device(char const
> > *devpath,
> >
> >      g_debug("  parse sysfs path '%s'", syspath);
> >
> > +    /* TODO: use is_disk_virtual() */
> >
> 
> just do it, no?

It's great that I put a note there otherwise I might have forgotten to
do it. ;)

> 
>      if (strstr(syspath, "/devices/virtual/block/")) {
> >          build_guest_fsinfo_for_virtual_device(syspath, fs, errp);
> >      } else {
> > @@ -1177,6 +1196,225 @@ static void build_guest_fsinfo_for_device(char
> > const *devpath,
> >      free(syspath);
> >  }
> >
> > +#ifdef CONFIG_LIBUDEV
> > +
> > +/*
> > + * Wrapper around build_guest_fsinfo_for_device() for getting just
> > + * the disk address.
> > + */
> > +static GuestDiskAddress *get_disk_address(const char *syspath, Error
> > **errp)
> > +{
> > +    g_autoptr(GuestFilesystemInfo) fs = NULL;
> > +
> > +    fs = g_new0(GuestFilesystemInfo, 1);
> >
> 
> Heap allocation / auto wasn't really necessary here, but ok.

I used it so that qapi_free_GuestFilesystemInfo() is called on function
exit in all cases. I am not sure if I could do that if `fs` were on the
stack.


> 
> 
> > +    build_guest_fsinfo_for_device(syspath, fs, errp);
> > +    if (fs->disk != NULL) {
> > +        return g_steal_pointer(&fs->disk->value);
> > +    }
> > +    return NULL;
> >
> 
> Could also be a onliner, but perhaps less readable.

Yeah, I prefer it this way.

> 
> +}
> > +
> > +static char *get_alias_for_syspath(const char *syspath)
> > +{
> > +    struct udev *udev = NULL;
> > +    struct udev_device *udevice = NULL;
> > +    char *ret = NULL;
> > +
> > +    udev = udev_new();
> >
> 
> I would have g_return_val_if_fail(udev != NULL, NULL); here as,
> 
> +    udevice = udev_device_new_from_syspath(udev, syspath);
> >
> 
> udev_device_new_from_syspath() might crash otherwise.

That is probably true. This may require fixes at other places too.

> 
> 
> > +    if (udev == NULL || udevice == NULL) {
> > +        g_debug("failed to query udev");
> > +    } else {
> > +        const char *alias = udev_device_get_property_value(
> > +            udevice, "DM_NAME");
> > +        if (alias != NULL && *alias != 0) {
> > +            ret = g_strdup(alias);
> >
> 
> g_strdup() works fine with NULL. Is there "" empty aliases? Why not report
> them too?

NULL means an error and empty alias means there is no alias. I will put
that in a comment there. In QAPI we have alias as optional which seems
preferable rather than always returning empty string.

> 
> +        }
> > +    }
> > +
> > +    udev_unref(udev);
> > +    udev_device_unref(udevice);
> > +    return ret;
> > +}
> > +
> > +static char *get_device_for_syspath(const char *syspath)
> > +{
> > +    struct udev *udev = NULL;
> > +    struct udev_device *udevice = NULL;
> > +    char *ret = NULL;
> > +
> > +    udev = udev_new();
> > +    udevice = udev_device_new_from_syspath(udev, syspath);
> > +    if (udev == NULL || udevice == NULL) {
> >
> 
> Same as above
> 
> +        g_debug("failed to query udev");
> > +    } else {
> > +        ret = g_strdup(udev_device_get_devnode(udevice));
> > +    }
> > +    udev_unref(udev);
> > +    udev_device_unref(udevice);
> > +    return ret;
> > +}
> > +
> >
> +GuestDiskInfoList *qmp_guest_get_disks(Error **errp)
> > +{
> > +    GuestDiskInfoList *item, *ret = NULL;
> > +    GuestDiskInfo *disk, *partition;
> > +    DIR *dp = NULL;
> > +    struct dirent *de = NULL;
> > +
> > +    g_debug("listing /sys/block directory");
> > +    dp = opendir("/sys/block");
> > +    if (dp == NULL) {
> > +        error_setg_errno(errp, errno, "Can't open directory
> > \"/sys/block\"");
> > +        return NULL;
> > +    }
> > +    while ((de = readdir(dp)) != NULL) {
> > +        g_autofree char *disk_dir = NULL, *line = NULL,
> > +            *size_dir = NULL, *slaves_dir = NULL;
> > +        struct dirent *de_disk, *de_slaves;
> > +        DIR *dp_disk = NULL, *dp_slaves = NULL;
> > +        FILE *fp = NULL;
> > +        size_t n = 0;
> > +        Error *local_err = NULL;
> > +        if (de->d_type != DT_LNK) {
> > +            g_debug("  skipping entry: %s", de->d_name);
> > +            continue;
> > +        }
> > +
> > +        /* Check size and skip zero-sized disks */
> > +        g_debug("  checking disk size");
> > +        size_dir = g_strdup_printf("/sys/block/%s/size", de->d_name);
> > +        fp = fopen(size_dir, "r");
> > +        if (!fp) {
> > +            g_debug("  failed to read disk size");
> > +            continue;
> > +        }
> > +        if (getline(&line, &n, fp) == -1) {
> > +            g_debug("  failed to read disk size");
> >
> 
> line: getline(3) "This buffer should be freed by the user program even if
> getline() failed."

That is handled by the g_autofree, or am I missing something? `line`
will get out of scope after every interation (even with continue). Or do
you prefer to have it explicit and free as soon as we don't need it?

> 
> +            fclose(fp);
> > +            continue;
> > +        }
> > +        fclose(fp);
> > +        if (strcmp(line, "0\n") == 0) {
> >
> 
> It would be slightly better to  defend against NULL crash here, with
> g_strcmp0()
> 
> +            g_debug("  skipping zero-sized disk");
> > +            continue;
> > +        }
> > +
> >
> 
> line is never freed?
> 
> +        g_debug("  adding %s", de->d_name);
> > +        disk_dir = g_strdup_printf("/sys/block/%s", de->d_name);
> > +        disk = g_new0(GuestDiskInfo, 1);
> > +        disk->name = get_device_for_syspath(disk_dir);
> > +        disk->partition = false;
> > +        disk->alias = get_alias_for_syspath(disk_dir);
> > +        if (disk->alias != NULL) {
> > +            disk->has_alias = true;
> > +        }
> >
> 
> Could be a single line too
> 
> +        item = g_new0(GuestDiskInfoList, 1);
> > +        item->value = disk;
> > +        item->next = ret;
> > +        ret = item;
> > +
> > +        /* Get address for non-virtual devices */
> > +        bool is_virtual = is_disk_virtual(disk_dir, &local_err);
> > +        if (local_err != NULL) {
> > +            g_debug("  failed to check disk path, ignoring error: %s",
> > +                error_get_pretty(local_err));
> > +            error_free(local_err);
> > +            local_err = NULL;
> >
> +            /* Don't try to get the address */
> > +            is_virtual = true;
> > +        }
> > +        if (!is_virtual) {
> > +            disk->address = get_disk_address(disk_dir, &local_err);
> > +            if (local_err != NULL) {
> > +                g_debug("  failed to get device info, ignoring error: %s",
> > +                    error_get_pretty(local_err));
> > +                error_free(local_err);
> > +                local_err = NULL;
> > +            } else if (disk->address != NULL) {
> > +                disk->has_address = true;
> > +            }
> > +        }
> > +
> > +        /* List slave disks */
> > +        slaves_dir = g_strdup_printf("%s/slaves", disk_dir);
> > +        g_debug("  listing entries in: %s", slaves_dir);
> > +        dp_slaves = opendir(slaves_dir);
> > +        while ((de_slaves = readdir(dp_slaves)) != NULL) {
> > +            g_autofree char *slave_dir = NULL;
> > +            char *slave_dev;
> > +            strList *slave_item = NULL;
> > +
> > +            if ((strcmp(".", de_slaves->d_name) == 0) ||
> > +                (strcmp("..", de_slaves->d_name) == 0)) {
> >
> +                continue;
> > +            }
> > +
> > +            /* Add slave disks */
> > +            slave_dir = g_strdup_printf("%s/%s",
> > +                slaves_dir, de_slaves->d_name);
> > +            slave_dev = get_device_for_syspath(slave_dir);
> > +            if (slave_dev != NULL) {
> > +                g_debug("  adding slave device: %s", slave_dev);
> > +                slave_item = g_new0(strList, 1);
> > +                slave_item->value = slave_dev;
> > +                slave_item->next = disk->slaves;
> > +                disk->slaves = slave_item;
> > +            }
> > +        }
> > +        closedir(dp_slaves);
> > +
> > +        /*
> > +         * Detect partitions subdirectory name is "<parent><number>" or
> > +         * "<parent>p<number>"
> > +         */
> > +        dp_disk = opendir(disk_dir);
> > +        while ((de_disk = readdir(dp_disk)) != NULL) {
> > +            size_t len;
> > +            g_autofree char *partition_dir = NULL;
> > +
> > +            if (!(de_disk->d_type & DT_DIR)) {
> > +                continue;
> > +            }
> > +
> > +            len = strlen(de->d_name);
> > +            if (!(strncmp(de->d_name, de_disk->d_name, len) == 0 &&
> > +                ((*(de_disk->d_name + len) == 'p' &&
> > +                isdigit(*(de_disk->d_name + len + 1))) ||
> > +                    isdigit(*(de_disk->d_name + len))))) {
> > +                continue;
> > +            }
> > +
> > +            partition_dir = g_strdup_printf("%s/%s",
> > +                disk_dir, de_disk->d_name);
> > +            partition = g_new0(GuestDiskInfo, 1);
> > +            partition->name = get_device_for_syspath(partition_dir);
> > +            partition->partition = true;
> > +            /* Add parent disk as slave for easier tracking of hierarchy
> > */
> > +            partition->slaves = g_new0(strList, 1);
> > +            partition->slaves->value = g_strdup(disk->name);
> > +
> > +            item = g_new0(GuestDiskInfoList, 1);
> > +            item->value = partition;
> > +            item->next = ret;
> > +            ret = item;
> > +
> > +        }
> > +        closedir(dp_disk);
> > +    }
> > +    return ret;
> > +}
> > +
> > +#else
> > +
> > +GuestDiskInfoList *qmp_guest_get_disks(Error **errp)
> > +{
> > +    error_setg(errp, QERR_UNSUPPORTED);
> > +    return NULL;
> > +}
> > +
> > +#endif
> > +
> >  /* Return a list of the disk device(s)' info which @mount lies on */
> >  static GuestFilesystemInfo *build_guest_fsinfo(struct FsMount *mount,
> >                                                 Error **errp)
> > @@ -2809,7 +3047,8 @@ GList *ga_command_blacklist_init(GList *blacklist)
> >          const char *list[] = {
> >              "guest-get-fsinfo", "guest-fsfreeze-status",
> >              "guest-fsfreeze-freeze", "guest-fsfreeze-freeze-list",
> > -            "guest-fsfreeze-thaw", "guest-get-fsinfo", NULL};
> > +            "guest-fsfreeze-thaw", "guest-get-fsinfo",
> > +            "guest-get-disks", NULL};
> >          char **p = (char **)list;
> >
> >          while (*p) {
> > @@ -3042,9 +3281,3 @@ GuestOSInfo *qmp_guest_get_osinfo(Error **errp)
> >
> >      return info;
> >  }
> > -
> > -GuestDiskInfoList *qmp_guest_get_disks(Error **errp)
> > -{
> > -    error_setg(errp, QERR_UNSUPPORTED);
> > -    return NULL;
> > -}
> > --
> > 2.25.0
> >
> >
> >
> 
> -- 
> Marc-André Lureau

-- 
Tomáš Golembiovský <tgolembi@redhat.com>