nfsd4: delay filling in write iovec array till after xdr decoding

Our server rejects compounds containing more than one write operation.
It's unclear whether this is really permitted by the spec; with 4.0,
it's possibly OK, with 4.1 (which has clearer limits on compound
parameters), it's probably not OK.  No client that we're aware of has
ever done this, but in theory it could be useful.

The source of the limitation: we need an array of iovecs to pass to the
write operation.  In the worst case that array of iovecs could have
hundreds of elements (the maximum rwsize divided by the page size), so
it's too big to put on the stack, or in each compound op.  So we instead
keep a single such array in the compound argument.

We fill in that array at the time we decode the xdr operation.

But we decode every op in the compound before executing any of them.  So
once we've used that array we can't decode another write.

If we instead delay filling in that array till the time we actually
perform the write, we can reuse it.

Another option might be to switch to decoding compound ops one at a
time.  I considered doing that, but it has a number of other side
effects, and I'd rather fix just this one problem for now.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
J. Bruce Fields 2012-11-15 14:52:19 -05:00
parent 70cc7f75b1
commit ffe1137ba7
4 changed files with 25 additions and 24 deletions

View File

@ -190,7 +190,7 @@ Nonstandard compound limitations:
ca_maxrequestsize request and a ca_maxresponsesize reply, so we may
fail to live up to the promise we made in CREATE_SESSION fore channel
negotiation.
* No more than one IO operation (read, write, readdir) allowed per
compound.
* No more than one read-like operation allowed per compound; encoding
replies that cross page boundaries (except for read data) not handled.
See also http://wiki.linux-nfs.org/wiki/index.php/Server_4.0_and_4.1_issues.

View File

@ -881,6 +881,24 @@ out:
return status;
}
static int fill_in_write_vector(struct kvec *vec, struct nfsd4_write *write)
{
int i = 1;
int buflen = write->wr_buflen;
vec[0].iov_base = write->wr_head.iov_base;
vec[0].iov_len = min_t(int, buflen, write->wr_head.iov_len);
buflen -= vec[0].iov_len;
while (buflen) {
vec[i].iov_base = page_address(write->wr_pagelist[i - 1]);
vec[i].iov_len = min_t(int, PAGE_SIZE, buflen);
buflen -= vec[i].iov_len;
i++;
}
return i;
}
static __be32
nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
struct nfsd4_write *write)
@ -889,6 +907,7 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
struct file *filp = NULL;
__be32 status = nfs_ok;
unsigned long cnt;
int nvecs;
/* no need to check permission - this will be done in nfsd_write() */
@ -911,8 +930,11 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
write->wr_how_written = write->wr_stable_how;
gen_boot_verifier(&write->wr_verifier);
nvecs = fill_in_write_vector(rqstp->rq_vec, write);
WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
status = nfsd_write(rqstp, &cstate->current_fh, filp,
write->wr_offset, rqstp->rq_vec, write->wr_vlen,
write->wr_offset, rqstp->rq_vec, nvecs,
&cnt, &write->wr_how_written);
if (filp)
fput(filp);

View File

@ -1139,24 +1139,6 @@ nfsd4_decode_verify(struct nfsd4_compoundargs *argp, struct nfsd4_verify *verify
DECODE_TAIL;
}
static int fill_in_write_vector(struct kvec *vec, struct nfsd4_write *write)
{
int i = 1;
int buflen = write->wr_buflen;
vec[0].iov_base = write->wr_head.iov_base;
vec[0].iov_len = min_t(int, buflen, write->wr_head.iov_len);
buflen -= vec[0].iov_len;
while (buflen) {
vec[i].iov_base = page_address(write->wr_pagelist[i - 1]);
vec[i].iov_len = min_t(int, PAGE_SIZE, buflen);
buflen -= vec[i].iov_len;
i++;
}
return i;
}
static __be32
nfsd4_decode_write(struct nfsd4_compoundargs *argp, struct nfsd4_write *write)
{
@ -1204,8 +1186,6 @@ nfsd4_decode_write(struct nfsd4_compoundargs *argp, struct nfsd4_write *write)
argp->end = argp->p + XDR_QUADLEN(PAGE_SIZE);
}
argp->p += XDR_QUADLEN(len);
write->wr_vlen = fill_in_write_vector(argp->rqstp->rq_vec, write);
WARN_ON_ONCE(write->wr_vlen > ARRAY_SIZE(argp->rqstp->rq_vec));
DECODE_TAIL;
}

View File

@ -385,7 +385,6 @@ struct nfsd4_write {
u64 wr_offset; /* request */
u32 wr_stable_how; /* request */
u32 wr_buflen; /* request */
int wr_vlen;
struct kvec wr_head;
struct page ** wr_pagelist; /* request */