Skip to content
Snippets Groups Projects
Select Git revision
  • 749da527b3e7bff92cc76b907bc222ef2df6fcdc
  • vme-testing default
  • ci-test
  • master
  • remoteproc
  • am625-sk-ov5640
  • pcal6534-upstreaming
  • lps22df-upstreaming
  • msc-upstreaming
  • imx8mp
  • iio/noa1305
  • vme-next
  • vme-next-4.14-rc4
  • v4.14-rc4
  • v4.14-rc3
  • v4.14-rc2
  • v4.14-rc1
  • v4.13
  • vme-next-4.13-rc7
  • v4.13-rc7
  • v4.13-rc6
  • v4.13-rc5
  • v4.13-rc4
  • v4.13-rc3
  • v4.13-rc2
  • v4.13-rc1
  • v4.12
  • v4.12-rc7
  • v4.12-rc6
  • v4.12-rc5
  • v4.12-rc4
  • v4.12-rc3
32 results

flexfilelayoutdev.c

Blame
  • flexfilelayoutdev.c 17.54 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     * Device operations for the pnfs nfs4 file layout driver.
     *
     * Copyright (c) 2014, Primary Data, Inc. All rights reserved.
     *
     * Tao Peng <bergwolf@primarydata.com>
     */
    
    #include <linux/nfs_fs.h>
    #include <linux/vmalloc.h>
    #include <linux/module.h>
    #include <linux/sunrpc/addr.h>
    
    #include "../internal.h"
    #include "../nfs4session.h"
    #include "flexfilelayout.h"
    
    #define NFSDBG_FACILITY		NFSDBG_PNFS_LD
    
    static unsigned int dataserver_timeo = NFS_DEF_TCP_RETRANS;
    static unsigned int dataserver_retrans;
    
    static bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg);
    
    void nfs4_ff_layout_put_deviceid(struct nfs4_ff_layout_ds *mirror_ds)
    {
    	if (!IS_ERR_OR_NULL(mirror_ds))
    		nfs4_put_deviceid_node(&mirror_ds->id_node);
    }
    
    void nfs4_ff_layout_free_deviceid(struct nfs4_ff_layout_ds *mirror_ds)
    {
    	nfs4_print_deviceid(&mirror_ds->id_node.deviceid);
    	nfs4_pnfs_ds_put(mirror_ds->ds);
    	kfree(mirror_ds->ds_versions);
    	kfree_rcu(mirror_ds, id_node.rcu);
    }
    
    /* Decode opaque device data and construct new_ds using it */
    struct nfs4_ff_layout_ds *
    nfs4_ff_alloc_deviceid_node(struct nfs_server *server, struct pnfs_device *pdev,
    			    gfp_t gfp_flags)
    {
    	struct xdr_stream stream;
    	struct xdr_buf buf;
    	struct page *scratch;
    	struct list_head dsaddrs;
    	struct nfs4_pnfs_ds_addr *da;
    	struct nfs4_ff_layout_ds *new_ds = NULL;
    	struct nfs4_ff_ds_version *ds_versions = NULL;
    	u32 mp_count;
    	u32 version_count;
    	__be32 *p;
    	int i, ret = -ENOMEM;
    
    	/* set up xdr stream */
    	scratch = alloc_page(gfp_flags);
    	if (!scratch)
    		goto out_err;
    
    	new_ds = kzalloc(sizeof(struct nfs4_ff_layout_ds), gfp_flags);
    	if (!new_ds)
    		goto out_scratch;
    
    	nfs4_init_deviceid_node(&new_ds->id_node,
    				server,
    				&pdev->dev_id);
    	INIT_LIST_HEAD(&dsaddrs);
    
    	xdr_init_decode_pages(&stream, &buf, pdev->pages, pdev->pglen);
    	xdr_set_scratch_buffer(&stream, page_address(scratch), PAGE_SIZE);
    
    	/* multipath count */
    	p = xdr_inline_decode(&stream, 4);
    	if (unlikely(!p))
    		goto out_err_drain_dsaddrs;
    	mp_count = be32_to_cpup(p);
    	dprintk("%s: multipath ds count %d\n", __func__, mp_count);
    
    	for (i = 0; i < mp_count; i++) {
    		/* multipath ds */
    		da = nfs4_decode_mp_ds_addr(server->nfs_client->cl_net,
    					    &stream, gfp_flags);
    		if (da)
    			list_add_tail(&da->da_node, &dsaddrs);
    	}
    	if (list_empty(&dsaddrs)) {
    		dprintk("%s: no suitable DS addresses found\n",
    			__func__);
    		ret = -ENOMEDIUM;
    		goto out_err_drain_dsaddrs;
    	}
    
    	/* version count */
    	p = xdr_inline_decode(&stream, 4);
    	if (unlikely(!p))
    		goto out_err_drain_dsaddrs;
    	version_count = be32_to_cpup(p);
    	dprintk("%s: version count %d\n", __func__, version_count);
    
    	ds_versions = kcalloc(version_count,
    			      sizeof(struct nfs4_ff_ds_version),
    			      gfp_flags);
    	if (!ds_versions)
    		goto out_scratch;
    
    	for (i = 0; i < version_count; i++) {
    		/* 20 = version(4) + minor_version(4) + rsize(4) + wsize(4) +
    		 * tightly_coupled(4) */
    		p = xdr_inline_decode(&stream, 20);
    		if (unlikely(!p))
    			goto out_err_drain_dsaddrs;
    		ds_versions[i].version = be32_to_cpup(p++);
    		ds_versions[i].minor_version = be32_to_cpup(p++);
    		ds_versions[i].rsize = nfs_block_size(be32_to_cpup(p++), NULL);
    		ds_versions[i].wsize = nfs_block_size(be32_to_cpup(p++), NULL);
    		ds_versions[i].tightly_coupled = be32_to_cpup(p);
    
    		if (ds_versions[i].rsize > NFS_MAX_FILE_IO_SIZE)
    			ds_versions[i].rsize = NFS_MAX_FILE_IO_SIZE;
    		if (ds_versions[i].wsize > NFS_MAX_FILE_IO_SIZE)
    			ds_versions[i].wsize = NFS_MAX_FILE_IO_SIZE;
    
    		/*
    		 * check for valid major/minor combination.
    		 * currently we support dataserver which talk:
    		 *   v3, v4.0, v4.1, v4.2
    		 */
    		if (!((ds_versions[i].version == 3 && ds_versions[i].minor_version == 0) ||
    			(ds_versions[i].version == 4 && ds_versions[i].minor_version < 3))) {
    			dprintk("%s: [%d] unsupported ds version %d-%d\n", __func__,
    				i, ds_versions[i].version,
    				ds_versions[i].minor_version);
    			ret = -EPROTONOSUPPORT;
    			goto out_err_drain_dsaddrs;
    		}
    
    		dprintk("%s: [%d] vers %u minor_ver %u rsize %u wsize %u coupled %d\n",
    			__func__, i, ds_versions[i].version,
    			ds_versions[i].minor_version,
    			ds_versions[i].rsize,
    			ds_versions[i].wsize,
    			ds_versions[i].tightly_coupled);
    	}
    
    	new_ds->ds_versions = ds_versions;
    	new_ds->ds_versions_cnt = version_count;
    
    	new_ds->ds = nfs4_pnfs_ds_add(&dsaddrs, gfp_flags);
    	if (!new_ds->ds)
    		goto out_err_drain_dsaddrs;
    
    	/* If DS was already in cache, free ds addrs */
    	while (!list_empty(&dsaddrs)) {
    		da = list_first_entry(&dsaddrs,
    				      struct nfs4_pnfs_ds_addr,
    				      da_node);
    		list_del_init(&da->da_node);
    		kfree(da->da_remotestr);
    		kfree(da);
    	}
    
    	__free_page(scratch);
    	return new_ds;
    
    out_err_drain_dsaddrs:
    	while (!list_empty(&dsaddrs)) {
    		da = list_first_entry(&dsaddrs, struct nfs4_pnfs_ds_addr,
    				      da_node);
    		list_del_init(&da->da_node);
    		kfree(da->da_remotestr);
    		kfree(da);
    	}
    
    	kfree(ds_versions);
    out_scratch:
    	__free_page(scratch);
    out_err:
    	kfree(new_ds);
    
    	dprintk("%s ERROR: returning %d\n", __func__, ret);
    	return NULL;
    }
    
    static void ff_layout_mark_devid_invalid(struct pnfs_layout_segment *lseg,
    		struct nfs4_deviceid_node *devid)
    {
    	nfs4_mark_deviceid_unavailable(devid);
    	if (!ff_layout_has_available_ds(lseg))
    		pnfs_error_mark_layout_for_return(lseg->pls_layout->plh_inode,
    				lseg);
    }
    
    static bool ff_layout_mirror_valid(struct pnfs_layout_segment *lseg,
    				   struct nfs4_ff_layout_mirror *mirror,
    				   bool create)
    {
    	if (mirror == NULL)
    		goto outerr;
    	if (mirror->mirror_ds == NULL) {
    		if (create) {
    			struct nfs4_deviceid_node *node;
    			struct pnfs_layout_hdr *lh = lseg->pls_layout;
    			struct nfs4_ff_layout_ds *mirror_ds = ERR_PTR(-ENODEV);
    
    			node = nfs4_find_get_deviceid(NFS_SERVER(lh->plh_inode),
    					&mirror->devid, lh->plh_lc_cred,
    					GFP_KERNEL);
    			if (node)
    				mirror_ds = FF_LAYOUT_MIRROR_DS(node);
    
    			/* check for race with another call to this function */
    			if (cmpxchg(&mirror->mirror_ds, NULL, mirror_ds) &&
    			    mirror_ds != ERR_PTR(-ENODEV))
    				nfs4_put_deviceid_node(node);
    		} else
    			goto outerr;
    	}
    
    	if (IS_ERR(mirror->mirror_ds))
    		goto outerr;
    
    	if (mirror->mirror_ds->ds == NULL) {
    		struct nfs4_deviceid_node *devid;
    		devid = &mirror->mirror_ds->id_node;
    		ff_layout_mark_devid_invalid(lseg, devid);
    		return false;
    	}
    	return true;
    outerr:
    	return false;
    }
    
    static void extend_ds_error(struct nfs4_ff_layout_ds_err *err,
    			    u64 offset, u64 length)
    {
    	u64 end;
    
    	end = max_t(u64, pnfs_end_offset(err->offset, err->length),
    		    pnfs_end_offset(offset, length));
    	err->offset = min_t(u64, err->offset, offset);
    	err->length = end - err->offset;
    }
    
    static int
    ff_ds_error_match(const struct nfs4_ff_layout_ds_err *e1,
    		const struct nfs4_ff_layout_ds_err *e2)
    {
    	int ret;
    
    	if (e1->opnum != e2->opnum)
    		return e1->opnum < e2->opnum ? -1 : 1;
    	if (e1->status != e2->status)
    		return e1->status < e2->status ? -1 : 1;
    	ret = memcmp(e1->stateid.data, e2->stateid.data,
    			sizeof(e1->stateid.data));
    	if (ret != 0)
    		return ret;
    	ret = memcmp(&e1->deviceid, &e2->deviceid, sizeof(e1->deviceid));
    	if (ret != 0)
    		return ret;
    	if (pnfs_end_offset(e1->offset, e1->length) < e2->offset)
    		return -1;
    	if (e1->offset > pnfs_end_offset(e2->offset, e2->length))
    		return 1;
    	/* If ranges overlap or are contiguous, they are the same */
    	return 0;
    }
    
    static void
    ff_layout_add_ds_error_locked(struct nfs4_flexfile_layout *flo,
    			      struct nfs4_ff_layout_ds_err *dserr)
    {
    	struct nfs4_ff_layout_ds_err *err, *tmp;
    	struct list_head *head = &flo->error_list;
    	int match;
    
    	/* Do insertion sort w/ merges */
    	list_for_each_entry_safe(err, tmp, &flo->error_list, list) {
    		match = ff_ds_error_match(err, dserr);
    		if (match < 0)
    			continue;
    		if (match > 0) {
    			/* Add entry "dserr" _before_ entry "err" */
    			head = &err->list;
    			break;
    		}
    		/* Entries match, so merge "err" into "dserr" */
    		extend_ds_error(dserr, err->offset, err->length);
    		list_replace(&err->list, &dserr->list);
    		kfree(err);
    		return;
    	}
    
    	list_add_tail(&dserr->list, head);
    }
    
    int ff_layout_track_ds_error(struct nfs4_flexfile_layout *flo,
    			     struct nfs4_ff_layout_mirror *mirror, u64 offset,
    			     u64 length, int status, enum nfs_opnum4 opnum,
    			     gfp_t gfp_flags)
    {
    	struct nfs4_ff_layout_ds_err *dserr;
    
    	if (status == 0)
    		return 0;
    
    	if (mirror->mirror_ds == NULL)
    		return -EINVAL;
    
    	dserr = kmalloc(sizeof(*dserr), gfp_flags);
    	if (!dserr)
    		return -ENOMEM;
    
    	INIT_LIST_HEAD(&dserr->list);
    	dserr->offset = offset;
    	dserr->length = length;
    	dserr->status = status;
    	dserr->opnum = opnum;
    	nfs4_stateid_copy(&dserr->stateid, &mirror->stateid);
    	memcpy(&dserr->deviceid, &mirror->mirror_ds->id_node.deviceid,
    	       NFS4_DEVICEID4_SIZE);
    
    	spin_lock(&flo->generic_hdr.plh_inode->i_lock);
    	ff_layout_add_ds_error_locked(flo, dserr);
    	spin_unlock(&flo->generic_hdr.plh_inode->i_lock);
    	return 0;
    }
    
    static const struct cred *
    ff_layout_get_mirror_cred(struct nfs4_ff_layout_mirror *mirror, u32 iomode)
    {
    	const struct cred *cred, __rcu **pcred;
    
    	if (iomode == IOMODE_READ)
    		pcred = &mirror->ro_cred;
    	else
    		pcred = &mirror->rw_cred;
    
    	rcu_read_lock();
    	do {
    		cred = rcu_dereference(*pcred);
    		if (!cred)
    			break;
    
    		cred = get_cred_rcu(cred);
    	} while(!cred);
    	rcu_read_unlock();
    	return cred;
    }
    
    struct nfs_fh *
    nfs4_ff_layout_select_ds_fh(struct nfs4_ff_layout_mirror *mirror)
    {
    	/* FIXME: For now assume there is only 1 version available for the DS */
    	return &mirror->fh_versions[0];
    }
    
    int
    nfs4_ff_layout_select_ds_stateid(struct pnfs_layout_segment *lseg,
    				u32 mirror_idx,
    				nfs4_stateid *stateid)
    {
    	struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, mirror_idx);
    
    	if (!ff_layout_mirror_valid(lseg, mirror, false)) {
    		pr_err_ratelimited("NFS: %s: No data server for mirror offset index %d\n",
    			__func__, mirror_idx);
    		goto out;
    	}
    
    	nfs4_stateid_copy(stateid, &mirror->stateid);
    	return 1;
    out:
    	return 0;
    }
    
    /**
     * nfs4_ff_layout_prepare_ds - prepare a DS connection for an RPC call
     * @lseg: the layout segment we're operating on
     * @mirror: layout mirror describing the DS to use
     * @fail_return: return layout on connect failure?
     *
     * Try to prepare a DS connection to accept an RPC call. This involves
     * selecting a mirror to use and connecting the client to it if it's not
     * already connected.
     *
     * Since we only need a single functioning mirror to satisfy a read, we don't
     * want to return the layout if there is one. For writes though, any down
     * mirror should result in a LAYOUTRETURN. @fail_return is how we distinguish
     * between the two cases.
     *
     * Returns a pointer to a connected DS object on success or NULL on failure.
     */
    struct nfs4_pnfs_ds *
    nfs4_ff_layout_prepare_ds(struct pnfs_layout_segment *lseg,
    			  struct nfs4_ff_layout_mirror *mirror,
    			  bool fail_return)
    {
    	struct nfs4_pnfs_ds *ds = NULL;
    	struct inode *ino = lseg->pls_layout->plh_inode;
    	struct nfs_server *s = NFS_SERVER(ino);
    	unsigned int max_payload;
    	int status;
    
    	if (!ff_layout_mirror_valid(lseg, mirror, true))
    		goto noconnect;
    
    	ds = mirror->mirror_ds->ds;
    	/* matching smp_wmb() in _nfs4_pnfs_v3/4_ds_connect */
    	smp_rmb();
    	if (ds->ds_clp)
    		goto out;
    
    	/* FIXME: For now we assume the server sent only one version of NFS
    	 * to use for the DS.
    	 */
    	status = nfs4_pnfs_ds_connect(s, ds, &mirror->mirror_ds->id_node,
    			     dataserver_timeo, dataserver_retrans,
    			     mirror->mirror_ds->ds_versions[0].version,
    			     mirror->mirror_ds->ds_versions[0].minor_version);
    
    	/* connect success, check rsize/wsize limit */
    	if (!status) {
    		max_payload =
    			nfs_block_size(rpc_max_payload(ds->ds_clp->cl_rpcclient),
    				       NULL);
    		if (mirror->mirror_ds->ds_versions[0].rsize > max_payload)
    			mirror->mirror_ds->ds_versions[0].rsize = max_payload;
    		if (mirror->mirror_ds->ds_versions[0].wsize > max_payload)
    			mirror->mirror_ds->ds_versions[0].wsize = max_payload;
    		goto out;
    	}
    noconnect:
    	ff_layout_track_ds_error(FF_LAYOUT_FROM_HDR(lseg->pls_layout),
    				 mirror, lseg->pls_range.offset,
    				 lseg->pls_range.length, NFS4ERR_NXIO,
    				 OP_ILLEGAL, GFP_NOIO);
    	ff_layout_send_layouterror(lseg);
    	if (fail_return || !ff_layout_has_available_ds(lseg))
    		pnfs_error_mark_layout_for_return(ino, lseg);
    	ds = NULL;
    out:
    	return ds;
    }
    
    const struct cred *
    ff_layout_get_ds_cred(struct pnfs_layout_segment *lseg, u32 ds_idx,
    		      const struct cred *mdscred)
    {
    	struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx);
    	const struct cred *cred;
    
    	if (mirror && !mirror->mirror_ds->ds_versions[0].tightly_coupled) {
    		cred = ff_layout_get_mirror_cred(mirror, lseg->pls_range.iomode);
    		if (!cred)
    			cred = get_cred(mdscred);
    	} else {
    		cred = get_cred(mdscred);
    	}
    	return cred;
    }
    
    /**
     * nfs4_ff_find_or_create_ds_client - Find or create a DS rpc client
     * @lseg: pointer to layout segment
     * @ds_idx: mirror index
     * @ds_clp: nfs_client for the DS
     * @inode: pointer to inode
     *
     * Find or create a DS rpc client with th MDS server rpc client auth flavor
     * in the nfs_client cl_ds_clients list.
     */
    struct rpc_clnt *
    nfs4_ff_find_or_create_ds_client(struct pnfs_layout_segment *lseg, u32 ds_idx,
    				 struct nfs_client *ds_clp, struct inode *inode)
    {
    	struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx);
    
    	switch (mirror->mirror_ds->ds_versions[0].version) {
    	case 3:
    		/* For NFSv3 DS, flavor is set when creating DS connections */
    		return ds_clp->cl_rpcclient;
    	case 4:
    		return nfs4_find_or_create_ds_client(ds_clp, inode);
    	default:
    		BUG();
    	}
    }
    
    void ff_layout_free_ds_ioerr(struct list_head *head)
    {
    	struct nfs4_ff_layout_ds_err *err;
    
    	while (!list_empty(head)) {
    		err = list_first_entry(head,
    				struct nfs4_ff_layout_ds_err,
    				list);
    		list_del(&err->list);
    		kfree(err);
    	}
    }
    
    /* called with inode i_lock held */
    int ff_layout_encode_ds_ioerr(struct xdr_stream *xdr, const struct list_head *head)
    {
    	struct nfs4_ff_layout_ds_err *err;
    	__be32 *p;
    
    	list_for_each_entry(err, head, list) {
    		/* offset(8) + length(8) + stateid(NFS4_STATEID_SIZE)
    		 * + array length + deviceid(NFS4_DEVICEID4_SIZE)
    		 * + status(4) + opnum(4)
    		 */
    		p = xdr_reserve_space(xdr,
    				28 + NFS4_STATEID_SIZE + NFS4_DEVICEID4_SIZE);
    		if (unlikely(!p))
    			return -ENOBUFS;
    		p = xdr_encode_hyper(p, err->offset);
    		p = xdr_encode_hyper(p, err->length);
    		p = xdr_encode_opaque_fixed(p, &err->stateid,
    					    NFS4_STATEID_SIZE);
    		/* Encode 1 error */
    		*p++ = cpu_to_be32(1);
    		p = xdr_encode_opaque_fixed(p, &err->deviceid,
    					    NFS4_DEVICEID4_SIZE);
    		*p++ = cpu_to_be32(err->status);
    		*p++ = cpu_to_be32(err->opnum);
    		dprintk("%s: offset %llu length %llu status %d op %d\n",
    			__func__, err->offset, err->length, err->status,
    			err->opnum);
    	}
    
    	return 0;
    }
    
    static
    unsigned int do_layout_fetch_ds_ioerr(struct pnfs_layout_hdr *lo,
    				      const struct pnfs_layout_range *range,
    				      struct list_head *head,
    				      unsigned int maxnum)
    {
    	struct nfs4_flexfile_layout *flo = FF_LAYOUT_FROM_HDR(lo);
    	struct inode *inode = lo->plh_inode;
    	struct nfs4_ff_layout_ds_err *err, *n;
    	unsigned int ret = 0;
    
    	spin_lock(&inode->i_lock);
    	list_for_each_entry_safe(err, n, &flo->error_list, list) {
    		if (!pnfs_is_range_intersecting(err->offset,
    				pnfs_end_offset(err->offset, err->length),
    				range->offset,
    				pnfs_end_offset(range->offset, range->length)))
    			continue;
    		if (!maxnum)
    			break;
    		list_move(&err->list, head);
    		maxnum--;
    		ret++;
    	}
    	spin_unlock(&inode->i_lock);
    	return ret;
    }
    
    unsigned int ff_layout_fetch_ds_ioerr(struct pnfs_layout_hdr *lo,
    				      const struct pnfs_layout_range *range,
    				      struct list_head *head,
    				      unsigned int maxnum)
    {
    	unsigned int ret;
    
    	ret = do_layout_fetch_ds_ioerr(lo, range, head, maxnum);
    	/* If we're over the max, discard all remaining entries */
    	if (ret == maxnum) {
    		LIST_HEAD(discard);
    		do_layout_fetch_ds_ioerr(lo, range, &discard, -1);
    		ff_layout_free_ds_ioerr(&discard);
    	}
    	return ret;
    }
    
    static bool ff_read_layout_has_available_ds(struct pnfs_layout_segment *lseg)
    {
    	struct nfs4_ff_layout_mirror *mirror;
    	struct nfs4_deviceid_node *devid;
    	u32 idx;
    
    	for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) {
    		mirror = FF_LAYOUT_COMP(lseg, idx);
    		if (mirror) {
    			if (!mirror->mirror_ds)
    				return true;
    			if (IS_ERR(mirror->mirror_ds))
    				continue;
    			devid = &mirror->mirror_ds->id_node;
    			if (!nfs4_test_deviceid_unavailable(devid))
    				return true;
    		}
    	}
    
    	return false;
    }
    
    static bool ff_rw_layout_has_available_ds(struct pnfs_layout_segment *lseg)
    {
    	struct nfs4_ff_layout_mirror *mirror;
    	struct nfs4_deviceid_node *devid;
    	u32 idx;
    
    	for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) {
    		mirror = FF_LAYOUT_COMP(lseg, idx);
    		if (!mirror || IS_ERR(mirror->mirror_ds))
    			return false;
    		if (!mirror->mirror_ds)
    			continue;
    		devid = &mirror->mirror_ds->id_node;
    		if (nfs4_test_deviceid_unavailable(devid))
    			return false;
    	}
    
    	return FF_LAYOUT_MIRROR_COUNT(lseg) != 0;
    }
    
    static bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg)
    {
    	if (lseg->pls_range.iomode == IOMODE_READ)
    		return  ff_read_layout_has_available_ds(lseg);
    	/* Note: RW layout needs all mirrors available */
    	return ff_rw_layout_has_available_ds(lseg);
    }
    
    bool ff_layout_avoid_mds_available_ds(struct pnfs_layout_segment *lseg)
    {
    	return ff_layout_no_fallback_to_mds(lseg) ||
    	       ff_layout_has_available_ds(lseg);
    }
    
    bool ff_layout_avoid_read_on_rw(struct pnfs_layout_segment *lseg)
    {
    	return lseg->pls_range.iomode == IOMODE_RW &&
    	       ff_layout_no_read_on_rw(lseg);
    }
    
    module_param(dataserver_retrans, uint, 0644);
    MODULE_PARM_DESC(dataserver_retrans, "The  number of times the NFSv4.1 client "
    			"retries a request before it attempts further "
    			" recovery  action.");
    module_param(dataserver_timeo, uint, 0644);
    MODULE_PARM_DESC(dataserver_timeo, "The time (in tenths of a second) the "
    			"NFSv4.1  client  waits for a response from a "
    			" data server before it retries an NFS request.");