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Re: [PATCH v3 3/5] tools/virtiofsd: xattr name mappings: Map server xatt
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH v3 3/5] tools/virtiofsd: xattr name mappings: Map server xattr names |
Date: |
Fri, 23 Oct 2020 15:49:12 +0100 |
User-agent: |
Mutt/1.14.6 (2020-07-11) |
* Vivek Goyal (vgoyal@redhat.com) wrote:
> On Wed, Oct 14, 2020 at 07:02:07PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@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 <dgilbert@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.
I always add a terminator in the parse as either a bad/ok, and was just
enforcing it - but I've changed it to a return -ENODATA that's probably
safer than the abort().
> > }
> > @@ -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.
Right, although the semantics are fuzzy anyway since someone can
come along and add/remove an xattr between the listxattr calls.
Dave
> Thanks
> Vivek
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
- Re: [PATCH v3 1/5] tools/virtiofsd: xattr name mappings: Add option, (continued)