Commit 895b00f6 authored by Marc-André Lureau's avatar Marc-André Lureau Committed by Michael Roth
Browse files

qga: flush explicitly when needed 

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: default avatarMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
* don't confuse {write,read}() with f{write,read}() in
  commit msg (Laszlo)
Signed-off-by: default avatarMichael Roth <mdroth@linux.vnet.ibm.com>
parent f2b608ab

qga/commands-posix.c

+37 −0
Original line number Diff line number Diff line
@@ -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;

    }

}