On Wed, Oct 14, 2020 at 07:02:07PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> Map xattr names coming from the server, i.e. the host filesystem;
> currently this is only from listxattr.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> tools/virtiofsd/passthrough_ll.c | 89 ++++++++++++++++++++++++++++++++
> 1 file changed, 89 insertions(+)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 57ebe17ed6..8406a2ae86 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2220,6 +2220,43 @@ static int xattr_map_client(const struct lo_data *lo,
> const char *client_name,
> }
> }
>
> + /* Shouldn't get here - rules should have an END_* - check
> parse_xattrmap */
> + abort();
> +}
> +
> +/*
> + * For use with listxattr where the server fs gives us a name and we may need
> + * to sanitize this for the client.
> + * Returns a pointer to the result in *out_name
> + * This is always the original string or the current string with some
> prefix
> + * removed; no reallocation is done.
> + * Returns 0 on success
> + * Can return -ENODATA to indicate the name should be dropped from the list.
> + */
> +static int xattr_map_server(const struct lo_data *lo, const char
> *server_name,
> + const char **out_name)
> +{
> + const XattrMapEntry *cur_entry;
> + const char *end;
> +
> + for (cur_entry = lo->xattr_map_list; ; cur_entry++) {
> + if ((cur_entry->flags & XATTR_MAP_FLAG_SERVER) &&
> + (strstart(server_name, cur_entry->prepend, &end))) {
> + if (cur_entry->flags & XATTR_MAP_FLAG_END_BAD) {
> + return -ENODATA;
> + }
> + if (cur_entry->flags & XATTR_MAP_FLAG_END_OK) {
> + *out_name = server_name;
> + return 0;
> + }
> + if (cur_entry->flags & XATTR_MAP_FLAG_PREFIX) {
> + /* Remove prefix */
> + *out_name = end;
> + return 0;
> + }
> + }
> + }
> +
> /* Shouldn't get here - rules should have an END_* */
> abort();
I am wondering why to put that restriction. If none of the rules match,
can't we just return as nothing has to be done.
> }
> @@ -2378,8 +2415,60 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t
> ino, size_t size)
> if (ret == 0) {
> goto out;
> }
> +
> + if (lo->xattr_map_list) {
> + /*
> + * Map the names back, some attributes might be dropped,
> + * some shortened, but not increased, so we shouldn't
> + * run out of room.
> + */
> + size_t out_index, in_index;
> + out_index = 0;
> + in_index = 0;
> + while (in_index < ret) {
> + const char *map_out;
> + char *in_ptr = value + in_index;
> + /* Length of current attribute name */
> + size_t in_len = strlen(value + in_index) + 1;
> +
> + int mapret = xattr_map_server(lo, in_ptr, &map_out);
> + if (mapret != -ENODATA && mapret != 0) {
> + /* Shouldn't happen */
> + saverr = -mapret;
> + goto out;
> + }
> + if (mapret == 0) {
> + /* Either unchanged, or truncated */
> + size_t out_len;
> + if (map_out != in_ptr) {
> + /* +1 copies the NIL */
> + out_len = strlen(map_out) + 1;
> + } else {
> + /* No change */
> + out_len = in_len;
> + }
> + /*
> + * Move result along, may still be needed for an
> unchanged
> + * entry if a previous entry was changed.
> + */
> + memmove(value + out_index, map_out, out_len);
> +
> + out_index += out_len;
> + }
> + in_index += in_len;
> + }
> + ret = out_index;
> + if (ret == 0) {
> + goto out;
> + }
> + }
> fuse_reply_buf(req, value, ret);
> } else {
> + /*
> + * xattrmap only ever shortens the result,
> + * so we don't need to do anything clever with the
> + * allocation length here.
> + */
> fuse_reply_xattr(req, ret);
Hmmm.., so this code returns the length of buffer which will fit xattrs.
So we will will changing the semantics a bit. Instead of returning
the exact size of buffer needed, we will be returning max size. I hope
its not a problem. Fixing it will be too expensive I guess.
Thanks
Vivek
