Re: [PATCH 1/7] qga/commands-posix: return fsinfo values directly as reported by statvfs

[Marc-André Lureau]

Hi

On Tue, Feb 27, 2024 at 4:38 PM Andrey Drobyshev
<andrey.drobyshev@virtuozzo.com> wrote:
>
>
>
> On 2/26/24 20:50, Konstantin Kostiuk wrote:
> >
> > Best Regards,
> > Konstantin Kostiuk.
> >
> >
> > On Mon, Feb 26, 2024 at 7:02 PM Andrey Drobyshev
> > <andrey.drobyshev@virtuozzo.com <mailto:andrey.drobyshev@virtuozzo.com>>
> > 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).
> >     These calculations might be obscure for the end user and require one to
> >     actually get into QGA source to understand how they're obtained. Let's
> >     just report the values f_blocks, f_bfree, f_bavail (in bytes) from
> >     statvfs() as they are, letting the user decide how to process them
> >     further.
> >
> >     Originally-by: Yuri Pudgorodskiy <yur@virtuozzo.com
> >     <mailto:yur@virtuozzo.com>>
> >     Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com
> >     <mailto:andrey.drobyshev@virtuozzo.com>>
> >     ---
> >      qga/commands-posix.c | 16 +++++++---------
> >      qga/qapi-schema.json | 11 +++++++----
> >      2 files changed, 14 insertions(+), 13 deletions(-)
> >
> >     diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> >     index 26008db497..752ef509d0 100644
> >     --- a/qga/commands-posix.c
> >     +++ b/qga/commands-posix.c
> >     @@ -1554,8 +1554,7 @@ static GuestFilesystemInfo
> >     *build_guest_fsinfo(strua5a0239ce5ct FsMount *mount,
> >                                                     Error **errp)
> >      {
> >          GuestFilesystemInfo *fs = g_malloc0(sizeof(*fs));
> >     -    struct statvfs buf;
> >     -    unsigned long used, nonroot_total, fr_size;
> >     +    struct statvfs st;
> >          char *devpath = g_strdup_printf("/sys/dev/block/%u:%u",
> >                                          mount->devmajor, mount->devminor);
> >
> >     @@ -1563,15 +1562,14 @@ static GuestFilesystemInfo
> >     *build_guest_fsinfo(struct FsMount *mount,
> >          fs->type = g_strdup(mount->devtype);
> >          build_guest_fsinfo_for_device(devpath, fs, errp);
> >
> >     -    if (statvfs(fs->mountpoint, &buf) == 0) {
> >     -        fr_size = buf.f_frsize;
> >     -        used = buf.f_blocks - buf.f_bfree;
> >     -        nonroot_total = used + buf.f_bavail;
> >     -        fs->used_bytes = used * fr_size;
> >     -        fs->total_bytes = nonroot_total * fr_size;
> >     +    if (statvfs(fs->mountpoint, &st) == 0) {
> >     +        fs->total_bytes = st.f_blocks * st.f_frsize;
> >     +        fs->free_bytes = st.f_bfree * st.f_frsize;
> >     +        fs->avail_bytes = st.f_bavail * st.f_frsize;
> >
> >              fs->has_total_bytes = true;
> >     -        fs->has_used_bytes = true;
> >     +        fs->has_free_bytes = true;
> >     +        fs->has_avail_bytes = true;
> >          }
> >
> >          g_free(devpath);
> >     diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
> >     index b8efe31897..1cce3c1df5 100644
> >     --- a/qga/qapi-schema.json
> >     +++ b/qga/qapi-schema.json
> >     @@ -1030,9 +1030,12 @@
> >      #
> >      # @type: file system type string
> >      #
> >     -# @used-bytes: file system used bytes (since 3.0)
> >     +# @total-bytes: total file system size in bytes (since 8.3)
> >      #
> >     -# @total-bytes: non-root file system total bytes (since 3.0)
> >     +# @free-bytes: amount of free space in file system in bytes (since 8.3)
> >
> >
> > I don't agree with this as it breaks backward compatibility. If we want
> > to get
> > these changes we should release a new version with both old and new fields
> > and mark old as deprecated to get a time for everyone who uses this
> > API updates its solutions.
> >
> > A similar thing was with replacing the 'blacklist' command line.
> > https://gitlab.com/qemu-project/qemu/-/commit/582a098e6ca00dd42f317dad8affd13e5a20bc42
> >  
> > <https://gitlab.com/qemu-project/qemu/-/commit/582a098e6ca00dd42f317dad8affd13e5a20bc42>
> > Currently, we support both 'blacklist' and 'block-rpcs' command line options
> > but the first one wrote a warning.
> >
>
> I agree that marking the old values as deprecated does make sense.
> Although my original intent with this patch is to make more sense of the
> existing names (e.g. total-bytes to indicate true fs size instead of
> just non-root fs).  If so, we'd eventually have to replace the original
> total-bytes value with the one having new semantics.  Or we could rename
> the existing value to smth like "total-bytes-nonroot".  But either way
> breaks backward compatibility after all.  How would you suggest to
> resolve it?


Why break backward compatibility? Don't break other systems (win32)
when you propose a patch.

QGA API aims to be cross-platform. Any system should be able to report
some kind of meaningful used and total disk space. I don't see much
reason to change that.

If we need Posix-specific values reported by statvfs(), we can have
extra optional struct/fields.

Fwiw, I find it more obscure to report statvfs values :) Perhaps we
should simply document better where those values are coming from,
instead of reporting more system-specific details.