From: Marc-André Lureau <marcandre.lur...@redhat.com> 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 <marcandre.lur...@redhat.com> --- 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 */ + 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); + if (ret == -1) { + error_setg_errno(errp, errno, "failed to seek file"); + return NULL; + } + gfh->writing = true; + } + buf = g_base64_decode(buf_b64, &buf_len); if (!has_count) { -- 2.5.0
