Re: [PATCH v3 1/7] qga: guest-get-fsinfo: add optional 'total-bytes-root' field

[Andrey Drobyshev]

On 3/19/24 19:37, Daniel P. Berrangé wrote:
> On Fri, Mar 15, 2024 at 02:29:40PM +0200, Andrey Drobyshev wrote:
>> Since the commit 25b5ff1a86 ("qga: add mountpoint usage info to
>> GuestFilesystemInfo") we have 2 values reported in guest-get-fsinfo:
>> used = (f_blocks - f_bfree), total = (f_blocks - f_bfree + f_bavail) as
>> returned by statvfs(3).  While on Windows guests that's all we can get
>> with GetDiskFreeSpaceExA(), on POSIX guests we might also be interested in
>> total file system size, as it's visible for root user.  Let's add an
>> optional field 'total-bytes-root' to GuestFilesystemInfo struct, which'd
>> only be reported on POSIX and represent f_blocks value as returned by
>> statvfs(3).
>>
>> While here, let's document better where those values come from in both
>> POSIX and Windows.
>>
>> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
>> ---
>>  qga/commands-posix.c |  2 ++
>>  qga/commands-win32.c |  1 +
>>  qga/qapi-schema.json | 12 +++++++++++-
>>  3 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
>> index 26008db497..8207c4c47e 100644
>> --- a/qga/commands-posix.c
>> +++ b/qga/commands-posix.c
>> @@ -1569,8 +1569,10 @@ static GuestFilesystemInfo *build_guest_fsinfo(struct 
>> FsMount *mount,
>>          nonroot_total = used + buf.f_bavail;
>>          fs->used_bytes = used * fr_size;
>>          fs->total_bytes = nonroot_total * fr_size;
>> +        fs->total_bytes_root = buf.f_blocks * fr_size;
>>  
>>          fs->has_total_bytes = true;
>> +        fs->has_total_bytes_root = true;
>>          fs->has_used_bytes = true;
>>      }
>>  
>> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
>> index a1015757d8..9e820aad8d 100644
>> --- a/qga/commands-win32.c
>> +++ b/qga/commands-win32.c
>> @@ -1143,6 +1143,7 @@ static GuestFilesystemInfo *build_guest_fsinfo(char 
>> *guid, Error **errp)
>>      fs = g_malloc(sizeof(*fs));
>>      fs->name = g_strdup(guid);
>>      fs->has_total_bytes = false;
>> +    fs->has_total_bytes_root = false;
> 
> Can we use GetDiskSpaceInformationA to return this information
> on Windows ? In contrast to GetDiskFreeSpaceExA(), the
> DISK_SPACE_INFORMATION struct details both the real sizes
> and the current user available sizes.
> 

It seems that this API has only been included in mingw64 recently:
https://github.com/mingw-w64/mingw-w64/commit/66546556

Apparently since it happened there hasn't been a new release of mingw64,
so the latest version v11.0.1 still doesn't have it.  So I guess we have
no choice but to leave Win fields as-is for now and switch to the new
API later.

>>      fs->has_used_bytes = false;
>>      if (len == 0) {
>>          fs->mountpoint = g_strdup("System Reserved");
>> diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
>> index b8efe31897..093a5ab602 100644
>> --- a/qga/qapi-schema.json
>> +++ b/qga/qapi-schema.json
>> @@ -1031,8 +1031,18 @@
>>  # @type: file system type string
>>  #
>>  # @used-bytes: file system used bytes (since 3.0)
>> +#     * POSIX: (f_blocks - f_bfree) * f_frsize, as returned by statvfs(3)
>> +#     * Windows: (TotalNumberOfBytes - TotalNumberOfFreeBytes), as returned
>> +#       by GetDiskFreeSpaceEx()
>>  #
>>  # @total-bytes: non-root file system total bytes (since 3.0)
>> +#     * POSIX: (f_blocks - f_bfree + f_bavail) * f_frsize, as returned by
>> +#       statvfs(3)
>> +#     * Windows: TotalNumberOfBytes, as returned by GetDiskFreeSpaceEx()
>> +#
>> +# @total-bytes-root: total file system size in bytes (as visible for a
>> +#     priviledged user) (since 8.3)
>> +#     * POSIX only: (f_blocks * f_frsize), returned by statvfs(3)
> 
> I tend to wonder whether it is really a good idea to document
> our specific implementation details in the public API
> 
> I might suggest
> 
>   @total-bytes: filesystem capacity in bytes for unprivileged users
>   @total-bytes-root: filesystem capacity in bytes for privileged users
>

My initial intent was to get rid of the necessity to dig into the
sources in order to understand what those values mean.  But since we're
discussing changes in the implementation, I guess it is wise not to
mention those details indeed.

> also should we call it 'total-bytes-privilegd', to avoid UNIX specific
> terminology.
> 

Agreed.

>>  #
>>  # @disk: an array of disk hardware information that the volume lies
>>  #     on, which may be empty if the disk type is not supported
>> @@ -1042,7 +1052,7 @@
>>  { 'struct': 'GuestFilesystemInfo',
>>    'data': {'name': 'str', 'mountpoint': 'str', 'type': 'str',
>>             '*used-bytes': 'uint64', '*total-bytes': 'uint64',
>> -           'disk': ['GuestDiskAddress']} }
>> +           '*total-bytes-root': 'uint64', 'disk': ['GuestDiskAddress']} }
>>  
>>  ##
>>  # @guest-get-fsinfo:
>> -- 
>> 2.39.3
>>
> 
> With regards,
> Daniel