ms-nfs41-client/daemon/pnfs_layout.c

/* Copyright (c) 2010
 * The Regents of the University of Michigan
 * All Rights Reserved
 *
 * Permission is granted to use, copy and redistribute this software
 * for noncommercial education and research purposes, so long as no
 * fee is charged, and so long as the name of the University of Michigan
 * is not used in any advertising or publicity pertaining to the use
 * or distribution of this software without specific, written prior
 * authorization.  Permission to modify or otherwise create derivative
 * works of this software is not granted.
 *
 * This software is provided as is, without representation or warranty
 * of any kind either express or implied, including without limitation
 * the implied warranties of merchantability, fitness for a particular
 * purpose, or noninfringement.  The Regents of the University of
 * Michigan shall not be liable for any damages, including special,
 * indirect, incidental, or consequential damages, with respect to any
 * claim arising out of or in connection with the use of the software,
 * even if it has been or is hereafter advised of the possibility of
 * such damages.
 */

#include <stdio.h>

#include "nfs41_ops.h"
#include "nfs41_callback.h"
#include "util.h"
#include "daemon_debug.h"


#define FLLVL 2 /* dprintf level for file layout logging */


/* pnfs_file_layout_list */
struct pnfs_file_layout_list {
    struct list_entry       head;
    CRITICAL_SECTION        lock;
};

#define layout_entry(pos) list_container(pos, pnfs_file_layout, entry)

static enum pnfs_status layout_create(
    IN const nfs41_fh *meta_fh,
    OUT pnfs_file_layout **layout_out)
{
    pnfs_file_layout *layout;
    enum pnfs_status status = PNFS_SUCCESS;

    layout = calloc(1, sizeof(pnfs_file_layout));
    if (layout == NULL) {
        status = PNFSERR_RESOURCES;
        goto out;
    }

    layout->layout.type = PNFS_LAYOUTTYPE_FILE;
    fh_copy(&layout->meta_fh, meta_fh);
    InitializeSRWLock(&layout->layout.lock);

    *layout_out = layout;
out:
    return status;
}

static void layout_free(
    IN pnfs_file_layout *layout)
{
    free(layout->filehandles.arr);
    free(layout);
}

static int layout_entry_compare(
    IN const struct list_entry *entry,
    IN const void *value)
{
    const pnfs_file_layout *layout = layout_entry(entry);
    const nfs41_fh *meta_fh = (const nfs41_fh*)value;
    const nfs41_fh *layout_fh = (const nfs41_fh*)&layout->meta_fh;
    const uint32_t diff = layout_fh->len - meta_fh->len;
    return diff ? diff : memcmp(layout_fh->fh, meta_fh->fh, meta_fh->len);
}

static enum pnfs_status layout_entry_find(
    IN struct pnfs_file_layout_list *layouts,
    IN const nfs41_fh *meta_fh,
    OUT struct list_entry **entry_out)
{
    *entry_out = list_search(&layouts->head, meta_fh, layout_entry_compare);
    return *entry_out ? PNFS_SUCCESS : PNFSERR_NO_LAYOUT;
}

enum pnfs_status pnfs_file_layout_list_create(
    OUT struct pnfs_file_layout_list **layouts_out)
{
    struct pnfs_file_layout_list *layouts;
    enum pnfs_status status = PNFS_SUCCESS;

    layouts = calloc(1, sizeof(struct pnfs_file_layout_list));
    if (layouts == NULL) {
        status = PNFSERR_RESOURCES;
        goto out;
    }
    list_init(&layouts->head);
    InitializeCriticalSection(&layouts->lock);
    *layouts_out = layouts;
out:
    return status;
}

void pnfs_file_layout_list_free(
    IN struct pnfs_file_layout_list *layouts)
{
    struct list_entry *entry, *tmp;

    EnterCriticalSection(&layouts->lock);

    list_for_each_tmp(entry, tmp, &layouts->head)
        layout_free(layout_entry(entry));

    LeaveCriticalSection(&layouts->lock);

    free(layouts);
}

static enum pnfs_status file_layout_find_or_create(
    IN struct pnfs_file_layout_list *layouts,
    IN const nfs41_fh *meta_fh,
    OUT pnfs_file_layout **layout_out)
{
    struct list_entry *entry;
    enum pnfs_status status;

    dprintf(FLLVL, "--> file_layout_find_or_create()\n");

    EnterCriticalSection(&layouts->lock);

    /* search for an existing layout */
    status = layout_entry_find(layouts, meta_fh, &entry);
    if (status) {
        /* create a new layout */
        pnfs_file_layout *layout;
        status = layout_create(meta_fh, &layout);
        if (status == PNFS_SUCCESS) {
            /* add it to the list */
            list_add_head(&layouts->head, &layout->entry);
            *layout_out = layout;

            dprintf(FLLVL, "<-- file_layout_find_or_create() "
                "returning new layout %p\n", layout);
        } else {
            dprintf(FLLVL, "<-- file_layout_find_or_create() "
                "returning %s\n", pnfs_error_string(status));
        }
    } else {
        *layout_out = layout_entry(entry);

        dprintf(FLLVL, "<-- file_layout_find_or_create() "
            "returning existing layout %p\n", *layout_out);
    }

    LeaveCriticalSection(&layouts->lock);
    return status;
}

static enum pnfs_status file_layout_find_and_delete(
    IN struct pnfs_file_layout_list *layouts,
    IN const nfs41_fh *meta_fh)
{
    struct list_entry *entry;
    enum pnfs_status status;

    dprintf(FLLVL, "--> file_layout_find_and_delete()\n");

    EnterCriticalSection(&layouts->lock);

    status = layout_entry_find(layouts, meta_fh, &entry);
    if (status == PNFS_SUCCESS) {
        list_remove(entry);
        layout_free(layout_entry(entry));
    }

    LeaveCriticalSection(&layouts->lock);

    dprintf(FLLVL, "<-- file_layout_find_and_delete() "
        "returning %s\n", pnfs_error_string(status));
    return status;
}


/* pnfs_file_layout */
static enum pnfs_status file_layout_fetch(
    IN OUT pnfs_file_layout *layout,
    IN nfs41_session *session,
    IN nfs41_path_fh *meta_file,
    IN stateid4 *state,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length)
{
    enum pnfs_status pnfsstat = PNFS_SUCCESS;
    enum nfsstat4 nfsstat;

    dprintf(FLLVL, "--> file_layout_fetch(%s, seqid=%u)\n",
        pnfs_iomode_string(iomode), layout->layout.state.seqid);

    nfsstat = pnfs_rpc_layoutget(session, meta_file,
        state, iomode, offset, length, layout);
    if (nfsstat) {
        dprintf(FLLVL, "pnfs_rpc_layoutget() failed with %s\n",
            nfs_error_string(nfsstat));
        pnfsstat = PNFSERR_NOT_SUPPORTED;
    }

    switch (nfsstat) {
    case NFS4_OK:
        /* mark granted and clear other flags */
        layout->layout.status = PNFS_LAYOUT_GRANTED;

        dprintf(FLLVL, "Received layout:\n");
        dprint_layout(FLLVL, layout);
        break;

    case NFS4ERR_BADIOMODE:
        /* don't try RW again */
        if (iomode == PNFS_IOMODE_RW)
            layout->layout.status |= PNFS_LAYOUT_NOT_RW;
        break;

    case NFS4ERR_LAYOUTUNAVAILABLE:
    case NFS4ERR_UNKNOWN_LAYOUTTYPE:
    case NFS4ERR_BADLAYOUT:
        /* don't try again at all */
        layout->layout.status |= PNFS_LAYOUT_UNAVAILABLE;
        break;
    }

    dprintf(FLLVL, "<-- file_layout_fetch() returning %s\n",
        pnfs_error_string(pnfsstat));
    return pnfsstat;
}

static bool_t layout_recalled(
    IN const pnfs_layout *layout)
{
    return (layout->status & PNFS_LAYOUT_RECALLED) != 0;
}

static bool_t layout_granted(
    IN const pnfs_layout *layout)
{
    return (layout->status & PNFS_LAYOUT_GRANTED) != 0;
}

static bool_t layout_not_rw(
    IN const pnfs_layout *layout)
{
    return (layout->status & PNFS_LAYOUT_NOT_RW) != 0;
}

static bool_t will_never_grant(
    IN const pnfs_layout *layout,
    IN enum pnfs_iomode iomode)
{
    return (layout->status & PNFS_LAYOUT_UNAVAILABLE) != 0
        || (iomode == PNFS_IOMODE_RW && layout_not_rw(layout));
}

static enum pnfs_status layout_grant_status(
    IN const pnfs_layout *layout,
    IN enum pnfs_iomode iomode)
{
    enum pnfs_status status = PNFS_PENDING;

    if (layout_recalled(layout)) {
        /* don't use a recalled layout */
        status = PNFSERR_LAYOUT_RECALLED;
    } else if (layout_granted(layout)) {
        /* the layout is granted; use it if it's compatible */
        status = PNFS_SUCCESS;
    } else if (will_never_grant(layout, iomode)) {
        /* an error from LAYOUTGET indicated that the server
         * won't ever grant this layout, so stop trying */
        status = PNFSERR_NOT_SUPPORTED;
    }
    return status;
}

static enum pnfs_status file_layout_cache(
    IN OUT pnfs_file_layout *layout,
    IN nfs41_session *session,
    IN nfs41_path_fh *meta_file,
    IN stateid4 *state,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length)
{
    enum pnfs_status status;

    /* use a shared lock to see if it's already been granted */
    AcquireSRWLockShared(&layout->layout.lock);
    status = layout_grant_status(&layout->layout, iomode);
    ReleaseSRWLockShared(&layout->layout.lock);

    if (status == PNFS_PENDING) {
        /* use an exclusive lock while attempting to get a new layout */
        AcquireSRWLockExclusive(&layout->layout.lock);

        status = layout_grant_status(&layout->layout, iomode);
        if (status == PNFS_PENDING) {
            /* if there's an existing layout stateid, use it */
            if (layout->layout.state.seqid)
                state = &layout->layout.state;

            if (!layout_not_rw(&layout->layout)) {
                /* try to get a RW layout first */
                status = file_layout_fetch(layout, session,
                    meta_file, state, PNFS_IOMODE_RW, offset, length);
            }

            if (status && iomode == PNFS_IOMODE_READ) {
                /* fall back on READ if necessary */
                status = file_layout_fetch(layout, session,
                    meta_file, state, iomode, offset, length);
            }
        }

        ReleaseSRWLockExclusive(&layout->layout.lock);
    }
    return status;
}

static enum pnfs_status layout_compatible(
    IN OUT pnfs_layout *layout,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length)
{
    enum pnfs_status status = PNFS_SUCCESS;

    AcquireSRWLockShared(&layout->lock);

    if (iomode == PNFS_IOMODE_RW && layout->iomode == PNFS_IOMODE_READ) {
        status = PNFSERR_NOT_SUPPORTED;
        goto out_unlock;
    }
    if (offset < layout->offset ||
        offset + length > layout->offset + layout->length) {
        status = PNFSERR_NOT_SUPPORTED;
        goto out_unlock;
    }
out_unlock:
    ReleaseSRWLockShared(&layout->lock);
    return status;
}

static enum pnfs_status file_device_status(
    IN const pnfs_layout *layout)
{
    enum pnfs_status status = PNFS_PENDING;

    if (layout_recalled(layout)) {
        /* don't fetch deviceinfo for a recalled layout */
        status = PNFSERR_LAYOUT_RECALLED;
    } else if (layout->status & PNFS_LAYOUT_HAS_DEVICE) {
        /* deviceinfo already cached */
        status = PNFS_SUCCESS;
    }
    return status;
}

static enum pnfs_status file_layout_device(
    IN OUT pnfs_file_layout *layout,
    IN nfs41_session *session)
{
    enum pnfs_status status = PNFS_PENDING;

    /* use a shared lock to see if we already have a device */
    AcquireSRWLockShared(&layout->layout.lock);
    status = file_device_status(&layout->layout);
    ReleaseSRWLockShared(&layout->layout.lock);

    if (status == PNFS_PENDING) {
        /* use an exclusive lock to look up device info */
        AcquireSRWLockExclusive(&layout->layout.lock);

        status = file_device_status(&layout->layout);
        if (status == PNFS_PENDING) {
            status = pnfs_file_device_get(session, session->client->devices,
                layout->deviceid, &layout->device);
            if (status == PNFS_SUCCESS)
                layout->layout.status |= PNFS_LAYOUT_HAS_DEVICE;
        }

        ReleaseSRWLockExclusive(&layout->layout.lock);
    }
    return status;
}

static enum pnfs_status file_layout_get(
    IN OUT pnfs_file_layout *layout,
    IN nfs41_session *session,
    IN nfs41_path_fh *meta_file,
    IN stateid4 *state,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length)
{
    enum pnfs_status status;

    /* request a range for the entire file */
    status = file_layout_cache(layout, session,
        meta_file, state, iomode, 0, NFS4_UINT64_MAX);
    if (status) {
        dprintf(FLLVL, "file_layout_cache() failed with %s\n",
            pnfs_error_string(status));
        goto out;
    }

    /* fail if we don't get everything we asked for */
    status = layout_compatible(&layout->layout, iomode, offset, length);
    if (status) {
        dprintf(FLLVL, "file_layout_compatible() failed with %s\n",
            pnfs_error_string(status));
        goto out;
    }

    /* make sure we have a device for the layout */
    status = file_layout_device(layout, session);
    if (status) {
        dprintf(FLLVL, "file_layout_device() failed with %s\n",
            pnfs_error_string(status));
        goto out;
    }
out:
    return status;
}

static enum pnfs_status layout_return_status(
    IN const pnfs_file_layout *layout)
{
    return (layout->layout.status & PNFS_LAYOUT_GRANTED) == 0
        ? PNFS_SUCCESS : PNFS_PENDING;
}

static enum pnfs_status file_layout_return(
    IN nfs41_session *session,
    IN nfs41_path_fh *file,
    IN pnfs_file_layout *layout)
{
    enum pnfs_status status;
    enum nfsstat4 nfsstat;

    dprintf(FLLVL, "--> file_layout_return()\n");

    /* under shared lock, determine whether we need to return the layout */
    AcquireSRWLockShared(&layout->layout.lock);
    status = layout_return_status(layout);
    ReleaseSRWLockShared(&layout->layout.lock);

    if (status == PNFS_PENDING) {
        /* under exclusive lock, return the layout and reset status flags */
        AcquireSRWLockExclusive(&layout->layout.lock);

        status = layout_return_status(layout);
        if (status == PNFS_PENDING) {
            /* reset the granted flag */
            layout->layout.status &= ~PNFS_LAYOUT_GRANTED;

            nfsstat = pnfs_rpc_layoutreturn(session, file, layout);
            if (nfsstat) {
                eprintf("pnfs_rpc_layoutreturn() failed with %s\n",
                    nfs_error_string(nfsstat));
                status = PNFSERR_NO_LAYOUT;
            } else {
                status = PNFS_SUCCESS;
            }
        }

        ReleaseSRWLockExclusive(&layout->layout.lock);
    }

    dprintf(FLLVL, "<-- file_layout_return() returning %s\n",
        pnfs_error_string(status));
    return status;
}


/* nfs41_open_state */
static enum pnfs_status client_supports_pnfs(
    IN nfs41_client *client)
{
    enum pnfs_status status;
    AcquireSRWLockShared(&client->exid_lock);
    status = client->roles & EXCHGID4_FLAG_USE_PNFS_MDS
        ? PNFS_SUCCESS : PNFSERR_NOT_SUPPORTED;
    ReleaseSRWLockShared(&client->exid_lock);
    return status;
}

static enum pnfs_status fs_supports_layout(
    IN const nfs41_superblock *superblock,
    IN enum pnfs_layout_type type)
{
    const uint32_t flag = 1 << (type - 1);
    return (superblock->layout_types & flag) == 0
        ? PNFSERR_NOT_SUPPORTED : PNFS_SUCCESS;
}

static enum pnfs_status open_state_layout_cached(
    IN nfs41_open_state *state,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length,
    OUT pnfs_file_layout **layout_out)
{
    enum pnfs_status status = PNFSERR_NO_LAYOUT;

    if (state->layout) {
        status = PNFS_SUCCESS;
        *layout_out = state->layout;

        dprintf(FLLVL, "pnfs_open_state_layout() found "
            "cached layout %p\n", *layout_out);
    }
    return status;
}

enum pnfs_status pnfs_open_state_layout(
    IN struct pnfs_file_layout_list *layouts,
    IN nfs41_session *session,
    IN nfs41_open_state *state,
    IN enum pnfs_iomode iomode,
    IN uint64_t offset,
    IN uint64_t length,
    OUT pnfs_file_layout **layout_out)
{
    pnfs_file_layout *layout;
    enum pnfs_status status;

    dprintf(FLLVL, "--> pnfs_open_state_layout()\n");

    status = client_supports_pnfs(session->client);
    if (status)
        goto out;
    status = fs_supports_layout(state->file.fh.superblock, PNFS_LAYOUTTYPE_FILE);
    if (status)
        goto out;

    /* under shared lock, check open state for cached layouts */
    AcquireSRWLockShared(&state->lock);
    status = open_state_layout_cached(state, iomode, offset, length, &layout);
    ReleaseSRWLockShared(&state->lock);

    if (status) {
        /* under exclusive lock, find or create a layout for this file */
        AcquireSRWLockExclusive(&state->lock);

        status = open_state_layout_cached(state, iomode, offset, length, &layout);
        if (status) {
            status = file_layout_find_or_create(layouts, &state->file.fh, &layout);
            if (status == PNFS_SUCCESS) {
                state->layout = layout;

                dprintf(FLLVL, "pnfs_open_state_layout() caching layout %p\n",
                    state->layout);
            }
        }

        ReleaseSRWLockExclusive(&state->lock);

        if (status)
            goto out;
    }

    /* make sure the layout can satisfy this request */
    status = file_layout_get(layout, session, &state->file,
        &state->stateid, iomode, offset, length);
    if (status) {
        dprintf(FLLVL, "file_layout_get() failed with %s\n",
            pnfs_error_string(status));
        goto out;
    }

    *layout_out = layout;
out:
    dprintf(FLLVL, "<-- pnfs_open_state_layout() returning %s\n",
        pnfs_error_string(status));
    return status;
}

void pnfs_open_state_close(
    IN nfs41_session *session,
    IN nfs41_open_state *state,
    IN bool_t remove)
{
    pnfs_file_layout *layout;
    bool_t return_on_close;
    enum pnfs_status status;

    AcquireSRWLockExclusive(&state->lock);
    layout = state->layout;
    state->layout = NULL;
    ReleaseSRWLockExclusive(&state->lock);

    if (layout) {
        /* check if we need to return the layout on close */
        AcquireSRWLockShared(&layout->layout.lock);
        return_on_close = layout->layout.return_on_close;
        ReleaseSRWLockShared(&layout->layout.lock);

        if (return_on_close) {
            status = file_layout_return(session, &state->file, layout);
            if (status)
                eprintf("file_layout_return() failed with %s\n",
                    pnfs_error_string(status));
        }
    }

    if (remove && session->client->layouts) {
        /* free the layout when the file is removed */
        file_layout_find_and_delete(session->client->layouts, &state->file.fh);
    }
}


/* pnfs_layout_recall */

/* expects the caller to have an exclusive lock */
static enum pnfs_status layout_recall_return(
    IN pnfs_layout *layout)
{
    dprintf(FLLVL, "layout_recall_return() 'forgetting' layout\n");

    /* since we're forgetful, we don't actually return the layout;
     * just zero the stateid since it won't be valid anymore */
    ZeroMemory(&layout->state, sizeof(layout->state));
    layout->status = 0;

    return PNFS_SUCCESS;
}

static enum pnfs_status file_layout_recall(
    IN pnfs_file_layout *layout,
    IN const struct cb_layoutrecall_args *recall)
{
    enum pnfs_status status = PNFS_SUCCESS;

    /* under an exclusive lock, flag the layout as recalled */
    AcquireSRWLockExclusive(&layout->layout.lock);

    if (layout->layout.io_count == 0) {
        /* if there is no pending io, return the layout now */
        status = layout_recall_return(&layout->layout);
    } else {
        /* flag the layout as recalled so it can be returned after io */
        layout->layout.status |= PNFS_LAYOUT_RECALLED;
        if (recall->changed)
            layout->layout.status |= PNFS_LAYOUT_CHANGED;
    }

    /* if we got a stateid, update the layout's seqid */
    if (recall->recall.type == PNFS_RETURN_FILE)
        layout->layout.state.seqid = recall->recall.args.file.stateid.seqid;

    ReleaseSRWLockExclusive(&layout->layout.lock);
    return status;
}

static enum pnfs_status file_layout_recall_file(
    IN struct pnfs_file_layout_list *layouts,
    IN const struct cb_layoutrecall_args *recall)
{
    struct list_entry *entry;
    enum pnfs_status status;

    dprintf(FLLVL, "--> file_layout_recall_file()\n");

    EnterCriticalSection(&layouts->lock);

    status = layout_entry_find(layouts, &recall->recall.args.file.fh, &entry);
    if (status == PNFS_SUCCESS)
        status = file_layout_recall(layout_entry(entry), recall);

    LeaveCriticalSection(&layouts->lock);

    dprintf(FLLVL, "<-- file_layout_recall_file() returning %s\n",
        pnfs_error_string(status));
    return status;
}

static bool_t fsid_matches(
    IN const nfs41_fsid *lhs,
    IN const nfs41_fsid *rhs)
{
    return lhs->major == rhs->major
        && lhs->minor == rhs->minor;
}

static enum pnfs_status file_layout_recall_fsid(
    IN struct pnfs_file_layout_list *layouts,
    IN const struct cb_layoutrecall_args *recall)
{
    struct list_entry *entry;
    pnfs_file_layout *layout;
    nfs41_fh *fh;
    enum pnfs_status status = PNFSERR_NO_LAYOUT;

    dprintf(FLLVL, "--> file_layout_recall_fsid(%llu, %llu)\n",
        recall->recall.args.fsid.major, recall->recall.args.fsid.minor);

    EnterCriticalSection(&layouts->lock);

    list_for_each(entry, &layouts->head) {
        layout = layout_entry(entry);
        /* no locks needed to read layout.meta_fh or superblock.fsid,
         * because they are only written once on creation */
        fh = &layout->meta_fh;
        if (fsid_matches(&recall->recall.args.fsid, &fh->superblock->fsid))
            status = file_layout_recall(layout, recall);
    }

    LeaveCriticalSection(&layouts->lock);

    dprintf(FLLVL, "<-- file_layout_recall_fsid() returning %s\n",
        pnfs_error_string(status));
    return status;
}

static enum pnfs_status file_layout_recall_all(
    IN struct pnfs_file_layout_list *layouts,
    IN const struct cb_layoutrecall_args *recall)
{
    struct list_entry *entry;
    enum pnfs_status status = PNFSERR_NO_LAYOUT;

    dprintf(FLLVL, "--> file_layout_recall_all()\n");

    EnterCriticalSection(&layouts->lock);

    list_for_each(entry, &layouts->head)
        status = file_layout_recall(layout_entry(entry), recall);

    LeaveCriticalSection(&layouts->lock);

    dprintf(FLLVL, "<-- file_layout_recall_all() returning %s\n",
        pnfs_error_string(status));
    return status;
}

enum pnfs_status pnfs_file_layout_recall(
    IN struct pnfs_file_layout_list *layouts,
    IN const struct cb_layoutrecall_args *recall)
{
    enum pnfs_status status = PNFS_SUCCESS;

    dprintf(FLLVL, "--> pnfs_file_layout_recall(%u, %s, %u)\n",
        recall->recall.type, pnfs_iomode_string(recall->iomode),
        recall->changed);

    if (recall->type != PNFS_LAYOUTTYPE_FILE) {
        dprintf(FLLVL, "invalid layout type %u (%s)!\n",
            recall->type, pnfs_layout_type_string(recall->type));
        status = PNFSERR_NOT_SUPPORTED;
        goto out;
    }

    switch (recall->recall.type) {
    case PNFS_RETURN_FILE:
        status = file_layout_recall_file(layouts, recall);
        break;
    case PNFS_RETURN_FSID:
        status = file_layout_recall_fsid(layouts, recall);
        break;
    case PNFS_RETURN_ALL:
        status = file_layout_recall_all(layouts, recall);
        break;

    default:
        dprintf(FLLVL, "invalid return type %u!\n", recall->recall);
        status = PNFSERR_NOT_SUPPORTED;
        goto out;
    }

    /* XXX: bulk layout recalls require invalidation of cached device info!
     * see CB_LAYOUTRECALL: http://tools.ietf.org/html/rfc5661#section-20.3.3 */
out:
    dprintf(FLLVL, "<-- pnfs_file_layout_recall() returning %s\n",
        pnfs_error_string(status));
    return status;
}


enum pnfs_status pnfs_layout_io_start(
    IN pnfs_layout *layout)
{
    enum pnfs_status status = PNFS_SUCCESS;

    AcquireSRWLockExclusive(&layout->lock);

    if (layout_recalled(layout)) {
        /* don't start any more io if the layout has been recalled */
        status = PNFSERR_LAYOUT_RECALLED;
        dprintf(FLLVL, "pnfs_layout_io_start() failed, layout was recalled\n");
    } else {
        /* take a reference on the layout, so that it won't be recalled
         * until all io is finished */
        layout->io_count++;
        dprintf(FLLVL, "pnfs_layout_io_start(): count -> %u\n",
            layout->io_count);
    }

    ReleaseSRWLockExclusive(&layout->lock);
    return status;
}

void pnfs_layout_io_finished(
    IN pnfs_layout *layout)
{
    AcquireSRWLockExclusive(&layout->lock);

    /* return the reference to signify that an io request is finished */
    layout->io_count--;
    dprintf(FLLVL, "pnfs_layout_io_finished() count -> %u\n",
        layout->io_count);

    if (layout->io_count > 0) /* more io pending */
        goto out_unlock;

    /* once all io is finished, check for layout recalls */
    if (layout->status & PNFS_LAYOUT_RECALLED)
        layout_recall_return(layout);

out_unlock:
    ReleaseSRWLockExclusive(&layout->lock);
}