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qga: flush explicitly when needed

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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, an fwrite() followed by an fread() 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.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
* don't confuse {write,read}() with f{write,read}() in
  commit msg (Laszlo)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
This commit is contained in:
Marc-André Lureau 2015-11-25 13:59:11 +01:00 committed by Michael Roth
parent f2b608ab80
commit 895b00f62a
1 changed files with 37 additions and 0 deletions
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37
qga/commands-posix.c
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@ -216,9 +216,16 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
}
}
typedef enum {
RW_STATE_NEW,
RW_STATE_READING,
RW_STATE_WRITING,
} RwState;
typedef struct GuestFileHandle {
uint64_t id;
FILE *fh;
RwState state;
QTAILQ_ENTRY(GuestFileHandle) next;
} GuestFileHandle;
@ -460,6 +467,17 @@ 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->state == RW_STATE_WRITING) {
int ret = fflush(fh);
if (ret == EOF) {
error_setg_errno(errp, errno, "failed to flush file");
return NULL;
}
gfh->state = RW_STATE_NEW;
}
buf = g_malloc0(count+1);
read_count = fread(buf, 1, count, fh);
if (ferror(fh)) {
@ -473,6 +491,7 @@ struct GuestFileRead *qmp_guest_file_read(int64_t handle, bool has_count,
if (read_count) {
read_data->buf_b64 = g_base64_encode(buf, read_count);
}
gfh->state = RW_STATE_READING;
}
g_free(buf);
clearerr(fh);
@ -496,6 +515,16 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle, const char *buf_b64,
}
fh = gfh->fh;
if (gfh->state == RW_STATE_READING) {
int ret = fseek(fh, 0, SEEK_CUR);
if (ret == -1) {
error_setg_errno(errp, errno, "failed to seek file");
return NULL;
}
gfh->state = RW_STATE_NEW;
}
buf = g_base64_decode(buf_b64, &buf_len);
if (!has_count) {
@ -515,6 +544,7 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle, const char *buf_b64,
write_data = g_new0(GuestFileWrite, 1);
write_data->count = write_count;
write_data->eof = feof(fh);
gfh->state = RW_STATE_WRITING;
}
g_free(buf);
clearerr(fh);
@ -538,10 +568,15 @@ struct GuestFileSeek *qmp_guest_file_seek(int64_t handle, int64_t offset,
ret = fseek(fh, offset, whence);
if (ret == -1) {
error_setg_errno(errp, errno, "failed to seek file");
if (errno == ESPIPE) {
/* file is non-seekable, stdio shouldn't be buffering anyways */
gfh->state = RW_STATE_NEW;
}
} else {
seek_data = g_new0(GuestFileSeek, 1);
seek_data->position = ftell(fh);
seek_data->eof = feof(fh);
gfh->state = RW_STATE_NEW;
}
clearerr(fh);
@ -562,6 +597,8 @@ void qmp_guest_file_flush(int64_t handle, Error **errp)
ret = fflush(fh);
if (ret == EOF) {
error_setg_errno(errp, errno, "failed to flush file");
} else {
gfh->state = RW_STATE_NEW;
}
}