On Tue, Jun 07, 2016 at 06:38:11AM -0400, Jeff Layton wrote:
> Currently, the layout driver selection code attempts to divine meaning
> from the order of the layout driver list sent by the server.
> Unfortunately, the spec doesn't place any significance on the order
> and the server is free to send them in any order it likes.
>
> Instead, set a list of preferred driver types in the kernel and have
> the selection code try them in order until it finds one that can be
> loaded.
>
> If we go through the whole list of preferred drivers and don't find one,
> then try any that weren't recognized in the first scan. This should
> allow the use of 3rd party and experimental drivers without needing to
> muck with the order of preference.
>
> For now, the order of preference is hardcoded, but it should be possible
> to make this configurable (via module param perhaps?).
>
> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
> ---
> fs/nfs/pnfs.c | 71 +++++++++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 50 insertions(+), 21 deletions(-)
>
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index b02cad9c04bf..3ec5f2b392b6 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -99,6 +99,21 @@ unset_pnfs_layoutdriver(struct nfs_server *nfss)
> }
>
> /*
> + * When the server sends a list of layout types, we choose one in the order
> + * given in the list below.
> + *
> + * FIXME: should this list be configurable via module_param or something?
> + */
> +static const u32 ld_prefs[] = {
> + LAYOUT_SCSI,
> + LAYOUT_BLOCK_VOLUME,
> + LAYOUT_OSD2_OBJECTS,
> + LAYOUT_FLEX_FILES,
> + LAYOUT_NFSV4_1_FILES,
> + 0
> +};
> +
> +/*
> * Try to set the server's pnfs module to the pnfs layout type specified by id.
> * Currently only one pNFS layout driver per filesystem is supported.
> *
> @@ -110,7 +125,7 @@ set_pnfs_layoutdriver(struct nfs_server *server, const struct nfs_fh *mntfh,
> {
> struct pnfs_layoutdriver_type *ld_type = NULL;
> u32 id;
> - int i;
> + int i, j;
>
> if (!(server->nfs_client->cl_exchange_flags &
> (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS))) {
> @@ -118,31 +133,45 @@ set_pnfs_layoutdriver(struct nfs_server *server, const struct nfs_fh *mntfh,
> __func__, server->nfs_client->cl_exchange_flags);
> goto out_no_driver;
> }
> - /*
> - * If server supports more than one layout types.
> - * By assuming, that server will put 'common default' as the first
> - * entry, try all following entries ibefore and fall back to the default
> - * if we did not found a matching one.
> - */
> - for(i = 1; i < NFS_MAX_LAYOUT_TYPES && ids[i] != 0; i++) {
> - id = ids[i];
> - request_module("%s-%u", LAYOUT_NFSV4_1_MODULE_PREFIX, id);
> - ld_type = find_pnfs_driver(id);
> - if(ld_type)
> - goto found_module;
>
> - dprintk("%s: No pNFS module found for %u.\n", __func__, id);
> + /* scan the list for each layout type in order of preference */
> + for (j = 0; ld_prefs[j] != 0; j++) {
> + for (i = 0; i < NFS_MAX_LAYOUT_TYPES && ids[i] != 0; i++) {
> + id = ids[i];
> +
> + if (ld_prefs[j] == id) {
> + request_module("%s-%u", LAYOUT_NFSV4_1_MODULE_PREFIX, id);
> + ld_type = find_pnfs_driver(id);
> + if (ld_type)
> + goto found_module;
> + }
> + }
> }
>
> - /*
> - * no other layout types found. Try default one.
> - */
> - id = ids[0];
> - request_module("%s-%u", LAYOUT_NFSV4_1_MODULE_PREFIX, id);
> - ld_type = find_pnfs_driver(id);
> + /* didn't find one -- make sure we try any that weren't in ld_prefs */
> + for (i = 0; i < NFS_MAX_LAYOUT_TYPES && ids[i] != 0; i++) {
> + bool match = false;
> +
> + id = ids[i];
> +
> + /* Was it in the prefs list? */
> + for (j = 0; ld_prefs[j] != 0; j++) {
> + if (ld_prefs[j] != id) {
> + match = true;
> + break;
> + }
> + }
This logic feels more complicated than necessary.
We're going out of our way to support (at this point purely theoretical)
3rd-party layout modules. When new layouts are develop, the chance
they'll be implementable with *no* changes to kernel code outside that
module seem small, and once you have to touch other code you may as well
update ld_prefs.
But anyway, if we want this, it might be easier to follow with logic
like:
1. sort the ids[] array so the known layouts are at the top, in
ld_prefs order.
2. try request_module() and find_pnfs_driver() in order on
the sorted ids[] array.
--b.
> +
> + if (!match) {
> + request_module("%s-%u", LAYOUT_NFSV4_1_MODULE_PREFIX, id);
> + ld_type = find_pnfs_driver(id);
> + if (ld_type)
> + goto found_module;
> + }
> + }
>
> if (!ld_type) {
> - dprintk("%s: No pNFS module found for %u.\n", __func__, id);
> + dprintk("%s: No pNFS module found!\n", __func__);
> goto out_no_driver;
> }
>
> --
> 2.5.5
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