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[Qemu-devel] [PATCH v2 1/2] qga: flush explicitly when needed
From: |
marcandre . lureau |
Subject: |
[Qemu-devel] [PATCH v2 1/2] qga: flush explicitly when needed |
Date: |
Tue, 24 Nov 2015 19:04:40 +0100 |
From: Marc-André Lureau <address@hidden>
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..d0228ce 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;
+
+ /* explicitly 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