The layout stateid will be invalidated once it holds no more layout
segments anyway.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

That's already being taken care of in pnfs_layout_remove_lseg().
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

If the server changed the layout stateid's "other" field, then
we should treat the old layout as being completely gone. In that
case, we want to clear the metadata such as scheduled layoutreturns.

Do this by calling pnfs_mark_layout_stateid_invalid().
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Ensure nfs42_layoutstat_done() layoutget don't open code layout stateid
invalidation.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

When determining which layout segments to return, we do want
pnfs_mark_matching_lsegs_return to check that they match the layout
sequence id. This ensures that we don't waste time if the server
is replaying a layout recall that has already been satisfied.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

In cases where we need to send a layoutreturn in order to propagate
an error, we should not tie that to a specific layout stateid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

When we return NFS_OK to the CB_LAYOUTRECALL, we are required to
send a layoutreturn that "completes" that layout recall request, using
the correct stateid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

We want to evaluate in this order:

If the client holds no layout for this inode, then return
NFS4ERR_NOMATCHING_LAYOUT; it probably forgot the layout.

If the client finds the inode among the list of layouts, but the corresponding
stateid has not yet been initialised, then return NFS4ERR_DELAY to ask the
server to retry once the outstanding LAYOUTGET is complete.

If the current layout stateid's "other" field does not match the recalled
stateid, return NFS4ERR_BAD_STATEID.

If already processing a layout recall with a newer stateid, return
NFS4ERR_OLD_STATEID. This can only happens for servers that are
non-compliant with the NFSv4.1 protocol.

If already processing a layout recall with an older stateid, return
NFS4ERR_DELAY to ask the server to retry once the outstanding
LAYOUTRETURN is complete. Again, this is technically incompliant with
the NFSv4.1 protocol.

If the current layout sequence id is newer than the recalled stateid's
sequence id, return NFS4ERR_OLD_STATEID. This too implies protocol
non-compliance.

If the current layout sequence id is older than the recalled stateid's
sequence id+1, return NFS4ERR_DELAY.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Currently, pnfs_set_layout_stateid() will update the layout sequence
id barrier only if the stateid itself is newer than the current
layout stateid. However in a situation where multiple LAYOUTGET calls
and a LAYOUTRETURN raced, it is entirely possible for one of the
LAYOUTGET to set the current stateid to something newer than the
LAYOUTRETURN that needs to set the barrier.

The fix is to allow the "update_barrier" flag to force a check as to
whether or not the barrier needs to be updated.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

If the layout stateid is invalid, then pnfs_set_layout_stateid() must
always initialise it.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Ensure that we don't carry over layoutreturn info from a previous
incarnation of this layout.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

If the layout was completely returned, then ignore the returned layout
stateid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

When bl_parse_deviceid() fails in bl_alloc_deviceid_node() on
blkdev_get_by_*() step we get an pnfs_block_dev struct that is
uninitialized except for bdev field which is set to whatever error
blkdev_get_by_*() returns.  bl_free_device() then tries to call
blkdev_put() if bdev is not 0 resulting in a wrong pointer dereference.

Fixing this by setting bdev in struct pnfs_block_dev only if we didn't
get an error from blkdev_get_by_*().
Signed-off-by: NArtem Savkov <asavkov@redhat.com>
Reviewed-by: NBenjamin Coddington <bcodding@redhat.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Avoid nfs return uuids/devices larger than maximum.
Signed-off-by: NKinglong Mee <kinglongmee@gmail.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Avoid a bad nfs server return an unaligned length of signature.
Signed-off-by: NKinglong Mee <kinglongmee@gmail.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Instead of reusing the wwn-* names for multipath devices nodes RHEL and
Fedora introduce new dm-mpath-uuid-* nodes with a slightly different
naming scheme.  Try these names first to ensure we always get a
multipath-capable device if it exists.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

The current code works with the standard udev/systemd names, but we'll have
to add another method in the next patch.  Refactor it into a separate helper
to make room for the new variant.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

This was fixed for the original block layout code a while ago, but also
needs to be fixed for the SCSI layout path.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

Olga Kornievskaia reports that the following test fails to trigger
an OPEN_DOWNGRADE on the wire, and only triggers the final CLOSE.

	fd0 = open(foo, RDRW)   -- should be open on the wire for "both"
	fd1 = open(foo, RDONLY)  -- should be open on the wire for "read"
	close(fd0) -- should trigger an open_downgrade
	read(fd1)
	close(fd1)

The issue is that we're missing a check for whether or not the current
state transitioned from an O_RDWR state as opposed to having transitioned
from a combination of O_RDONLY and O_WRONLY.
Reported-by: NOlga Kornievskaia <aglo@umich.edu>
Fixes: cd9288ff ("NFSv4: Fix another bug in the close/open_downgrade code")
Cc: stable@vger.kernel.org # 2.6.33+
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

In "NFSv4: Move dentry instantiation into the NFSv4-specific atomic open code"
unconditional d_drop() after the ->open_context() had been removed.  It had
been correct for success cases (there ->open_context() itself had been doing
dcache manipulations), but not for error ones.  Only one of those (ENOENT)
got a compensatory d_drop() added in that commit, but in fact it should've
been done for all errors.  As it is, the case of O_CREAT non-exclusive open
on a hashed negative dentry racing with e.g. symlink creation from another
client ended up with ->open_context() getting an error and proceeding to
call nfs_lookup().  On a hashed dentry, which would've instantly triggered
BUG_ON() in d_materialise_unique() (or, these days, its equivalent in
d_splice_alias()).

Cc: stable@vger.kernel.org # v3.10+
Tested-by: NOleg Drokin <green@linuxhacker.ru>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

If we don't set the mode correctly in nfs_init_locked(), then there is
potential for a race with a second call to nfs_fhget that will cause
inode aliasing.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

According to RFC5661, section 12.5.3. the layout stateid is no longer
valid once the client no longer holds any layout segments. Ensure that
we mark it invalid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Since commit 0bcbf039, nfs_readpage_release() has been used to
unlock the page in the read code.

Fixes: 0bcbf039 ("nfs: handle request add failure properly")
Cc: stable@vger.kernel.org # v4.5+
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

pnfs_generic_commit_cancel_empty_pagelist calls nfs_commitdata_release,
but that is wrong: nfs_commitdata_release puts the open context, something
that isn't valid until nfs_init_commit is called, which is never the case
when pnfs_generic_commit_cancel_empty_pagelist is called.

This was introduced in "nfs: avoid race that crashes nfs_init_commit".
Signed-off-by: NWeston Andros Adamson <dros@primarydata.com>
Cc: stable@vger.kernel.org
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Commit e8d975e7 ("fixing infinite OPEN loop in 4.0 stateid recovery")
introduced access to state after it was just potentially freed by
nfs4_put_open_state leading to a random data corruption somewhere.

BUG: unable to handle kernel paging request at ffff88004941ee40
IP: [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
PGD 3501067 PUD 3504067 PMD 6ff37067 PTE 800000004941e060
Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
Modules linked in: loop rpcsec_gss_krb5 acpi_cpufreq tpm_tis joydev i2c_piix4 pcspkr tpm virtio_console nfsd ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops floppy serio_raw virtio_blk drm
CPU: 6 PID: 2161 Comm: 192.168.10.253- Not tainted 4.7.0-rc1-vm-nfs+ #112
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff8800463dcd00 ti: ffff88003ff48000 task.ti: ffff88003ff48000
RIP: 0010:[<ffffffff813baf01>]  [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
RSP: 0018:ffff88003ff4bd68  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffff81a49900 RCX: 00000000000000e8
RDX: 00000000000000e8 RSI: ffff8800418b9930 RDI: ffff880040c96c88
RBP: ffff88003ff4bdf8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880040c96c98
R13: ffff88004941ee20 R14: ffff88004941ee40 R15: ffff88004941ee00
FS:  0000000000000000(0000) GS:ffff88006d000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88004941ee40 CR3: 0000000060b0b000 CR4: 00000000000006e0
Stack:
 ffffffff813baad5 ffff8800463dcd00 ffff880000000001 ffffffff810e6b68
 ffff880043ddbc88 ffff8800418b9800 ffff8800418b98c8 ffff88004941ee48
 ffff880040c96c90 ffff880040c96c00 ffff880040c96c20 ffff880040c96c40
Call Trace:
 [<ffffffff813baad5>] ? nfs4_do_reclaim+0x35/0x740
 [<ffffffff810e6b68>] ? trace_hardirqs_on_caller+0x128/0x1b0
 [<ffffffff813bb7cd>] nfs4_run_state_manager+0x5ed/0xa40
 [<ffffffff813bb1e0>] ? nfs4_do_reclaim+0x740/0x740
 [<ffffffff813bb1e0>] ? nfs4_do_reclaim+0x740/0x740
 [<ffffffff810af0d1>] kthread+0x101/0x120
 [<ffffffff810e6b68>] ? trace_hardirqs_on_caller+0x128/0x1b0
 [<ffffffff818843af>] ret_from_fork+0x1f/0x40
 [<ffffffff810aefd0>] ? kthread_create_on_node+0x250/0x250
Code: 65 80 4c 8b b5 78 ff ff ff e8 fc 88 4c 00 48 8b 7d 88 e8 13 67 d2 ff 49 8b 47 40 a8 02 0f 84 d3 01 00 00 4c 89 ff e8 7f f9 ff ff <f0> 41 80 26 7f 48 8b 7d c8 e8 b1 84 4c 00 e9 39 fd ff ff 3d e6
RIP  [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
 RSP <ffff88003ff4bd68>
CR2: ffff88004941ee40
Signed-off-by: NOleg Drokin <green@linuxhacker.ru>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

if we read or wrote something, we must report it
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@poochiereds.net>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

We must call nfs4_handle_exception() on BAD_STATEID errors. The only
exception is if the stateid argument turns out to be a layout stateid
that is declared invalid.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@poochiereds.net>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@poochiereds.net>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@poochiereds.net>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

nfs4_handle_exception() relies on the caller setting the 'inode' field
in the struct nfs4_exception argument when the error applies to a
delegation.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NJeff Layton <jlayton@poochiereds.net>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Older versions of gcc don't understand named initializers inside a
anonymous structure or union member.  It can be worked around by adding
the bracin gin the initializer for the anonymous member.

Without this, gcc 4.4.4 will fail the build with

    CC      fs/nfs/nfs4state.o
  fs/nfs/nfs4state.c:69: error: unknown field ‘data’ specified in initializer
  fs/nfs/nfs4state.c:69: warning: missing braces around initializer
  fs/nfs/nfs4state.c:69: warning: (near initialization for ‘zero_stateid.<anonymous>.data’)
  make[2]: *** [fs/nfs/nfs4state.o] Error 1

introduced in commit 93b717fd ("NFSv4: Label stateids with the type")
Reported-and-tested-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Anna Schumaker <Anna.Schumaker@netapp.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

preparation for similar switch in ->setxattr() (see the next commit for
rationale).
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

As flexfiles has FF_FLAGS_NO_READ_IO, there is a need to generically
support enforcing that a IOMODE_RW segment will not allow READ I/O.
Signed-off-by: NTom Haynes <loghyr@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Signed-off-by: NTom Haynes <loghyr@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

The mds can inform the client not to use the IOMODE_RW layout
segment for doing READs. I.e., it is basically a
IOMODE_WRITE layout segment.

It would do this to not interfere with the WRITEs.
Signed-off-by: NTom Haynes <loghyr@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

Since the patch "NFS: Allow multiple commit requests in flight per file"
we can run multiple simultaneous commits on the same inode.  This
introduced a race over collecting pages to commit that made it possible
to call nfs_init_commit() with an empty list - which causes crashes like
the one below.

The fix is to catch this race and avoid calling nfs_init_commit and
initiate_commit when there is no work to do.

Here is the crash:

[600522.076832] BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
[600522.078475] IP: [<ffffffffa0479e72>] nfs_init_commit+0x22/0x130 [nfs]
[600522.078745] PGD 4272b1067 PUD 4272cb067 PMD 0
[600522.078972] Oops: 0000 [#1] SMP
[600522.079204] Modules linked in: nfsv3 nfs_layout_flexfiles rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache dcdbas ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw vmw_vsock_vmci_transport vsock bonding ipmi_devintf ipmi_msghandler coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel ppdev vmw_balloon parport_pc parport acpi_cpufreq vmw_vmci i2c_piix4 shpchp nfsd auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c vmwgfx drm_kms_helper ttm drm crc32c_intel serio_raw vmxnet3
[600522.081380]  vmw_pvscsi ata_generic pata_acpi
[600522.081809] CPU: 3 PID: 15667 Comm: /usr/bin/python Not tainted 4.1.9-100.pd.88.el7.x86_64 #1
[600522.082281] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 09/30/2014
[600522.082814] task: ffff8800bbbfa780 ti: ffff88042ae84000 task.ti: ffff88042ae84000
[600522.083378] RIP: 0010:[<ffffffffa0479e72>]  [<ffffffffa0479e72>] nfs_init_commit+0x22/0x130 [nfs]
[600522.083973] RSP: 0018:ffff88042ae87438  EFLAGS: 00010246
[600522.084571] RAX: 0000000000000000 RBX: ffff880003485e40 RCX: ffff88042ae87588
[600522.085188] RDX: 0000000000000000 RSI: ffff88042ae874b0 RDI: ffff880003485e40
[600522.085756] RBP: ffff88042ae87448 R08: ffff880003486010 R09: ffff88042ae874b0
[600522.086332] R10: 0000000000000000 R11: 0000000000000005 R12: ffff88042ae872d0
[600522.086905] R13: ffff88042ae874b0 R14: ffff880003485e40 R15: ffff88042704c840
[600522.087484] FS:  00007f4728ff2740(0000) GS:ffff88043fd80000(0000) knlGS:0000000000000000
[600522.088070] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[600522.088663] CR2: 0000000000000040 CR3: 000000042b6aa000 CR4: 00000000001406e0
[600522.089327] Stack:
[600522.089926]  0000000000000001 ffff88042ae87588 ffff88042ae874f8 ffffffffa04f09fa
[600522.090549]  0000000000017840 0000000000017840 ffff88042ae87588 ffff8803258d9930
[600522.091169]  ffff88042ae87578 ffffffffa0563d80 0000000000000000 ffff88042704c840
[600522.091789] Call Trace:
[600522.092420]  [<ffffffffa04f09fa>] pnfs_generic_commit_pagelist+0x1da/0x320 [nfsv4]
[600522.093052]  [<ffffffffa0563d80>] ? ff_layout_commit_prepare_v3+0x30/0x30 [nfs_layout_flexfiles]
[600522.093696]  [<ffffffffa0562645>] ff_layout_commit_pagelist+0x15/0x20 [nfs_layout_flexfiles]
[600522.094359]  [<ffffffffa047bc78>] nfs_generic_commit_list+0xe8/0x120 [nfs]
[600522.095032]  [<ffffffffa047bd6a>] nfs_commit_inode+0xba/0x110 [nfs]
[600522.095719]  [<ffffffffa046ac54>] nfs_release_page+0x44/0xd0 [nfs]
[600522.096410]  [<ffffffff811a8122>] try_to_release_page+0x32/0x50
[600522.097109]  [<ffffffff811bd4f1>] shrink_page_list+0x961/0xb30
[600522.097812]  [<ffffffff811bdced>] shrink_inactive_list+0x1cd/0x550
[600522.098530]  [<ffffffff811bea65>] shrink_lruvec+0x635/0x840
[600522.099250]  [<ffffffff811bed60>] shrink_zone+0xf0/0x2f0
[600522.099974]  [<ffffffff811bf312>] do_try_to_free_pages+0x192/0x470
[600522.100709]  [<ffffffff811bf6ca>] try_to_free_pages+0xda/0x170
[600522.101464]  [<ffffffff811b2198>] __alloc_pages_nodemask+0x588/0x970
[600522.102235]  [<ffffffff811fbbd5>] alloc_pages_vma+0xb5/0x230
[600522.103000]  [<ffffffff813a1589>] ? cpumask_any_but+0x39/0x50
[600522.103774]  [<ffffffff811d6115>] wp_page_copy.isra.55+0x95/0x490
[600522.104558]  [<ffffffff810e3438>] ? __wake_up+0x48/0x60
[600522.105357]  [<ffffffff811d7d3b>] do_wp_page+0xab/0x4f0
[600522.106137]  [<ffffffff810a1bbb>] ? release_task+0x36b/0x470
[600522.106902]  [<ffffffff8126dbd7>] ? eventfd_ctx_read+0x67/0x1c0
[600522.107659]  [<ffffffff811da2a8>] handle_mm_fault+0xc78/0x1900
[600522.108431]  [<ffffffff81067ef1>] __do_page_fault+0x181/0x420
[600522.109173]  [<ffffffff811446a6>] ? __audit_syscall_exit+0x1e6/0x280
[600522.109893]  [<ffffffff810681c0>] do_page_fault+0x30/0x80
[600522.110594]  [<ffffffff81024f36>] ? syscall_trace_leave+0xc6/0x120
[600522.111288]  [<ffffffff81790a58>] page_fault+0x28/0x30
[600522.111947] Code: 5d c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 4c 8d 87 d0 01 00 00 48 89 e5 53 48 89 fb 48 83 ec 08 4c 8b 0e 49 8b 41 18 4c 39 ce <48> 8b 40 40 4c 8b 50 30 74 24 48 8b 87 d0 01 00 00 48 8b 7e 08
[600522.113343] RIP  [<ffffffffa0479e72>] nfs_init_commit+0x22/0x130 [nfs]
[600522.114003]  RSP <ffff88042ae87438>
[600522.114636] CR2: 0000000000000040

Fixes: af7cf057 (NFS: Allow multiple commit requests in flight per file)
CC: stable@vger.kernel.org
Signed-off-by: NWeston Andros Adamson <dros@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

nfs_create_request() doesn't return NULL, it returns error pointers.

Fixes: 67911c8f ('NFS: Add nfs_commit_file()')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

It can return NULL if layoutgets are blocked currently. Fix it to return
-EAGAIN in that case, so we can properly handle it in pnfs_update_layout.

Also, clean up and simplify the error handling -- eliminate "status" and
just use "lseg".
Signed-off-by: NJeff Layton <jeff.layton@primarydata.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>