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Re: [Qemu-devel] [PATCH 1/2] qga: flush implicitely when needed
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] qga: flush implicitely when needed |
Date: |
Tue, 24 Nov 2015 10:15:26 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
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.
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.
>
> 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.
> + 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>
> 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
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