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Re: [Qemu-devel] [PATCH 1/2] qga: flush implicitely when needed
From: |
Marc-André Lureau |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] qga: flush implicitely when needed |
Date: |
Tue, 24 Nov 2015 12:52:40 -0500 (EST) |
Hi
----- Original Message -----
> On 11/24/2015 09:34 AM, address@hidden wrote:
> > From: Marc-André Lureau <address@hidden>
>
> In the subject: s/implicitely/implicitly/ if you are fixing the typo, or
> s/implicitely/explicitly/ if you are trying to make it match what the
> patch actually does.
>
ok, I'll switch to explicitely (it depends on the point of view, I was
commenting from the qga API user pov, but I get your point)
> No 0/2 cover letter? ALL multi-patch series should include a cover
> letter, as it is easier on tooling to be able to base series-wide
> conversations on the cover letter.
>
Ok, I didn't know. If I don't have much to say in cover letter, I usually drop
it. I'll keep it then.
> >
> > According to the specification:
> > http://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
> >
> > "the application shall ensure that output is not directly followed by
> > input without an intervening call to fflush() or to a file positioning
> > function (fseek(), fsetpos(), or rewind()), and input is not directly
> > followed by output without an intervening call to a file positioning
> > function, unless the input operation encounters end-of-file."
> >
> > Without this change, a write() followed by a read() may lose the
> > previously written content, as shown in the following test.
> >
> > Fixes:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1210246
> >
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> > qga/commands-posix.c | 22 ++++++++++++++++++++++
> > 1 file changed, 22 insertions(+)
> >
> > diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> > index 0ebd473..3c86a4e 100644
> > --- a/qga/commands-posix.c
> > +++ b/qga/commands-posix.c
> > @@ -219,6 +219,7 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns,
> > Error **errp)
> > typedef struct GuestFileHandle {
> > uint64_t id;
> > FILE *fh;
> > + bool writing;
> > QTAILQ_ENTRY(GuestFileHandle) next;
> > } GuestFileHandle;
> >
> > @@ -460,6 +461,17 @@ struct GuestFileRead *qmp_guest_file_read(int64_t
> > handle, bool has_count,
> > }
> >
> > fh = gfh->fh;
> > +
> > + /* implicitely flush when switching from writing to reading */
>
> Again, s/implicitely/explicitly/
>
> > + if (gfh->writing) {
> > + int ret = fflush(fh);
> > + if (ret == EOF) {
> > + error_setg_errno(errp, errno, "failed to flush file");
> > + return NULL;
> > + }
> > + gfh->writing = false;
> > + }
> > +
> > buf = g_malloc0(count+1);
> > read_count = fread(buf, 1, count, fh);
> > if (ferror(fh)) {
> > @@ -496,6 +508,16 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle,
> > const char *buf_b64,
> > }
> >
> > fh = gfh->fh;
> > +
> > + if (!gfh->writing) {
> > + int ret = fseek(fh, 0, SEEK_CUR);
>
> Seems a bit odd to use fflush() in one place and fseek() in the other,
> but the net result is the same either way.
"and input is not directly followed by output without an intervening call to a
file positioning function, unless the input operation encounters end-of-file."
so I tried to follow what the spec said.
>
> > + if (ret == -1) {
> > + error_setg_errno(errp, errno, "failed to seek file");
> > + return NULL;
> > + }
> > + gfh->writing = true;
> > + }
> > +
>
> With typos fixed,
> Reviewed-by: Eric Blake <address@hidden>
thanks
>
> > buf = g_base64_decode(buf_b64, &buf_len);
> >
> > if (!has_count) {
> >
>
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>