On Wed, Oct 18, 2023 at 10:25 AM Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
> On Wed, Oct 18, 2023 at 09:33:40AM -0400, Jeff Layton wrote:
> > On Wed, 2023-10-18 at 08:56 -0400, Chuck Lever wrote:
> > > On Tue, Oct 17, 2023 at 05:30:44PM -0400, Benjamin Coddington wrote:
> > > > Expose a per-mount knob in sysfs to set the READDIR requested attributes
> > > > for a non-plus READDIR request.
> > > >
> > > > For example:
> > > >
> > > > echo 0x800 0x800000 0x0 > /sys/fs/nfs/0\:57/v4_readdir_attrs
> > > >
I understand why you're not adding a keyword for each attribute
requested in a readdir, but would it be possible to have a single
magic keyword like "reset" or "default" that is an alias for reverting
to the default attributes?
> > > > .. will revert the client to only request rdattr_error and
> > > > mounted_on_fileid for any non "plus" READDIR, as before the patch
> > > > preceeding this one in this series. This provides existing installations
> > > > an option to fix a potential performance regression that may occur after
> > > > NFS clients update to request additional default READDIR attributes.
> > > >
> > > > Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> > > > ---
> > > > fs/nfs/client.c | 2 +
> > > > fs/nfs/nfs4client.c | 4 ++
> > > > fs/nfs/nfs4proc.c | 1 +
> > > > fs/nfs/nfs4xdr.c | 7 ++--
> > > > fs/nfs/sysfs.c | 81 +++++++++++++++++++++++++++++++++++++++
> > > > include/linux/nfs_fs_sb.h | 1 +
> > > > include/linux/nfs_xdr.h | 1 +
> > > > 7 files changed, 93 insertions(+), 4 deletions(-)
> > >
> > > Admittedly, it would be much easier for humans to use if the API was
> > > based on the symbolic names of the bits rather than a triplet of raw
> > > hexadecimal values.
> > >
> >
> > I think there are some significant footguns with this interface. It'd be
> > very easy to set this wrong and get weird behavior. OTOH, we could push
> > that complexity into userland and provide some sort of script in nfs-
> > utils for tuning this.
> >
> > That said...
> >
> > When we look at interfaces like this, we have to consider that they may
> > be around for a long, long time (decades, even), and people will come to
> > rely on them to do strange things that are difficult for us to support.
> > If we have someone saying that their READDIR performance slowed down, we
> > now have to grab those settings from this sysfs file and validate them
> > when trying to help them.
> >
> > Personally, I'd prefer a simple binary "make it work the old way"
> > switch, if we're concerned about performance regressions here. I think
> > that's the sort of thing that is simple to explain to admins that are
> > suffering from this problem and (more importantly) the sort of setting
> > we can later remove when it's no longer needed.
> >
> > Adding this sort of fine-grained knob will create more problems than it
> > solves, as people will (inevitably) use it incorrectly.
>
> Totally agree with this assessment. It will get baked into wacky
> knowledge base articles for decades. Voice of experience here ;-)
>
> It's not yet clear sysadmins will even need a switch like this, so I
> would go further and say you should hold off on merging anything
> like it until there is an actual reported need for it.
>
> Now, full control over that bitmap is still very neat thing for
> experimentation by NFS developers. Hiding this behind a Kconfig
> option would let you merge it but then turn it off in production
> kernels.
Definitely a neat thing to have, but I'm also in favor of hiding it
behind a kconfig option to start.
Anna
>
>
> > > > diff --git a/fs/nfs/client.c b/fs/nfs/client.c
> > > > index 44eca51b2808..e9aa1fd4335f 100644
> > > > --- a/fs/nfs/client.c
> > > > +++ b/fs/nfs/client.c
> > > > @@ -922,6 +922,8 @@ void nfs_server_copy_userdata(struct nfs_server *target, struct nfs_server *sour
> > > > target->options = source->options;
> > > > target->auth_info = source->auth_info;
> > > > target->port = source->port;
> > > > + memcpy(target->readdir_attrs, source->readdir_attrs,
> > > > + sizeof(target->readdir_attrs));
> > > > }
> > > > EXPORT_SYMBOL_GPL(nfs_server_copy_userdata);
> > > >
> > > > diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
> > > > index 11e3a285594c..3bbfb4244c14 100644
> > > > --- a/fs/nfs/nfs4client.c
> > > > +++ b/fs/nfs/nfs4client.c
> > > > @@ -1115,6 +1115,10 @@ static int nfs4_server_common_setup(struct nfs_server *server,
> > > >
> > > > nfs4_server_set_init_caps(server);
> > > >
> > > > + /* Default (non-plus) v4 readdir attributes */
> > > > + server->readdir_attrs[0] = FATTR4_WORD0_TYPE|FATTR4_WORD0_RDATTR_ERROR;
> > > > + server->readdir_attrs[1] = FATTR4_WORD1_MOUNTED_ON_FILEID;
> > > > +
> > > > /* Probe the root fh to retrieve its FSID and filehandle */
> > > > error = nfs4_get_rootfh(server, mntfh, auth_probe);
> > > > if (error < 0)
> > > > diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> > > > index 7016eaadf555..0f0028de7941 100644
> > > > --- a/fs/nfs/nfs4proc.c
> > > > +++ b/fs/nfs/nfs4proc.c
> > > > @@ -5113,6 +5113,7 @@ static int _nfs4_proc_readdir(struct nfs_readdir_arg *nr_arg,
> > > > .pgbase = 0,
> > > > .count = nr_arg->page_len,
> > > > .plus = nr_arg->plus,
> > > > + .server = server,
> > > > };
> > > > struct nfs4_readdir_res res;
> > > > struct rpc_message msg = {
> > > > diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
> > > > index 7200d6f7cd7b..45a9b40b801e 100644
> > > > --- a/fs/nfs/nfs4xdr.c
> > > > +++ b/fs/nfs/nfs4xdr.c
> > > > @@ -1601,16 +1601,15 @@ static void encode_read(struct xdr_stream *xdr, const struct nfs_pgio_args *args
> > > >
> > > > static void encode_readdir(struct xdr_stream *xdr, const struct nfs4_readdir_arg *readdir, struct rpc_rqst *req, struct compound_hdr *hdr)
> > > > {
> > > > - uint32_t attrs[3] = {
> > > > - FATTR4_WORD0_TYPE|FATTR4_WORD0_RDATTR_ERROR,
> > > > - FATTR4_WORD1_MOUNTED_ON_FILEID,
> > > > - };
> > > > + uint32_t attrs[3];
> > > > uint32_t dircount = readdir->count;
> > > > uint32_t maxcount = readdir->count;
> > > > __be32 *p, verf[2];
> > > > uint32_t attrlen = 0;
> > > > unsigned int i;
> > > >
> > > > + memcpy(attrs, readdir->server->readdir_attrs, sizeof(attrs));
> > > > +
> > > > if (readdir->plus) {
> > > > attrs[0] |= FATTR4_WORD0_CHANGE|FATTR4_WORD0_SIZE|
> > > > FATTR4_WORD0_FSID|FATTR4_WORD0_FILEHANDLE|FATTR4_WORD0_FILEID;
> > > > diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
> > > > index bf378ecd5d9f..6d4f52bf47b3 100644
> > > > --- a/fs/nfs/sysfs.c
> > > > +++ b/fs/nfs/sysfs.c
> > > > @@ -270,7 +270,82 @@ shutdown_store(struct kobject *kobj, struct kobj_attribute *attr,
> > > > return count;
> > > > }
> > > >
> > > > +static ssize_t
> > > > +v4_readdir_attrs_show(struct kobject *kobj, struct kobj_attribute *attr,
> > > > + char *buf)
> > > > +{
> > > > + struct nfs_server *server;
> > > > + server = container_of(kobj, struct nfs_server, kobj);
> > > > +
> > > > + return sysfs_emit(buf, "0x%x 0x%x 0x%x\n",
> > > > + server->readdir_attrs[0],
> > > > + server->readdir_attrs[1],
> > > > + server->readdir_attrs[2]);
> > > > +}
> > > > +
> > > > +static ssize_t
> > > > +v4_readdir_attrs_store(struct kobject *kobj, struct kobj_attribute *attr,
> > > > + const char *buf, size_t count)
> > > > +{
> > > > + struct nfs_server *server;
> > > > + u32 attrs[3];
> > > > + char p[36], *v;
> > > > + size_t token = 0;
> > > > + int i;
> > > > +
> > > > + if (count > 36)
> > > > + return -EINVAL;
> > > > +
> > > > + v = strncpy(p, buf, count);
> > > > +
> > > > + for (i = 0; i < 3; i++) {
> > > > + token += strcspn(v, " ") + 1;
> > > > + if (token > 34)
> > > > + return -EINVAL;
> > > > +
> > > > + p[token - 1] = '\0';
> > > > + if (kstrtoint(v, 0, &attrs[i]))
> > > > + return -EINVAL;
> > > > + v = &p[token];
> > > > + }
> > > > +
> > > > + /* Allow only what we decode - see decode_getfattr_attrs() */
> > > > + if (attrs[0] & ~(FATTR4_WORD0_TYPE |
> > > > + FATTR4_WORD0_CHANGE |
> > > > + FATTR4_WORD0_SIZE |
> > > > + FATTR4_WORD0_FSID |
> > > > + FATTR4_WORD0_RDATTR_ERROR |
> > > > + FATTR4_WORD0_FILEHANDLE |
> > > > + FATTR4_WORD0_FILEID |
> > > > + FATTR4_WORD0_FS_LOCATIONS) ||
> > > > + attrs[1] & ~(FATTR4_WORD1_MODE |
> > > > + FATTR4_WORD1_NUMLINKS |
> > > > + FATTR4_WORD1_OWNER |
> > > > + FATTR4_WORD1_OWNER_GROUP |
> > > > + FATTR4_WORD1_RAWDEV |
> > > > + FATTR4_WORD1_SPACE_USED |
> > > > + FATTR4_WORD1_TIME_ACCESS |
> > > > + FATTR4_WORD1_TIME_METADATA |
> > > > + FATTR4_WORD1_TIME_MODIFY |
> > > > + FATTR4_WORD1_MOUNTED_ON_FILEID) ||
> > > > + attrs[2] & ~(FATTR4_WORD2_MDSTHRESHOLD |
> > > > + FATTR4_WORD2_SECURITY_LABEL))
> > > > + return -EINVAL;
> > > > +
> > > > + server = container_of(kobj, struct nfs_server, kobj);
> > > > +
> > > > + if (attrs[0])
> > > > + server->readdir_attrs[0] = attrs[0];
> > > > + if (attrs[1])
> > > > + server->readdir_attrs[1] = attrs[1];
> > > > + if (attrs[2])
> > > > + server->readdir_attrs[2] = attrs[2];
> > > > +
> > > > + return count;
> > > > +}
> > > > +
> > > > static struct kobj_attribute nfs_sysfs_attr_shutdown = __ATTR_RW(shutdown);
> > > > +static struct kobj_attribute nfs_sysfs_attr_v4_readdir_attrs = __ATTR_RW(v4_readdir_attrs);
> > > >
> > > > #define RPC_CLIENT_NAME_SIZE 64
> > > >
> > > > @@ -325,6 +400,12 @@ void nfs_sysfs_add_server(struct nfs_server *server)
> > > > if (ret < 0)
> > > > pr_warn("NFS: sysfs_create_file_ns for server-%d failed (%d)\n",
> > > > server->s_sysfs_id, ret);
> > > > +
> > > > + ret = sysfs_create_file_ns(&server->kobj, &nfs_sysfs_attr_v4_readdir_attrs.attr,
> > > > + nfs_netns_server_namespace(&server->kobj));
> > > > + if (ret < 0)
> > > > + pr_warn("NFS: sysfs_create_file_ns for server-%d failed (%d)\n",
> > > > + server->s_sysfs_id, ret);
> > > > }
> > > > EXPORT_SYMBOL_GPL(nfs_sysfs_add_server);
> > > >
> > > > diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
> > > > index cd628c4b011e..db87261b7cd7 100644
> > > > --- a/include/linux/nfs_fs_sb.h
> > > > +++ b/include/linux/nfs_fs_sb.h
> > > > @@ -219,6 +219,7 @@ struct nfs_server {
> > > > of change attribute, size, ctime
> > > > and mtime attributes supported by
> > > > the server */
> > > > + u32 readdir_attrs[3]; /* V4 tuneable default readdir attrs */
> > > > u32 acl_bitmask; /* V4 bitmask representing the ACEs
> > > > that are supported on this
> > > > filesystem */
> > > > diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
> > > > index 12bbb5c63664..e05d861b1788 100644
> > > > --- a/include/linux/nfs_xdr.h
> > > > +++ b/include/linux/nfs_xdr.h
> > > > @@ -1142,6 +1142,7 @@ struct nfs4_readdir_arg {
> > > > struct page ** pages; /* zero-copy data */
> > > > unsigned int pgbase; /* zero-copy data */
> > > > const u32 * bitmask;
> > > > + const struct nfs_server *server;
> > > > bool plus;
> > > > };
> > > >
> > > > --
> > > > 2.41.0
> > > >
> > >
> >
> > --
> > Jeff Layton <jlayton@xxxxxxxxxx>
>
> --
> Chuck Lever
