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nfsd4: "backfill" using write_bytes_to_xdr_buf

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Normally xdr encoding proceeds in a single pass from start of a buffer
to end, but sometimes we have to write a few bytes to an earlier
position.

Use write_bytes_to_xdr_buf for these cases rather than saving a pointer
to write to.  We plan to rewrite xdr_reserve_space to handle encoding
across page boundaries using a scratch buffer, and don't want to risk
writing to a pointer that was contained in a scratch buffer.

Also it will no longer be safe to calculate lengths by subtracting two
pointers, so use xdr_buf offsets instead.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
J. Bruce Fields 2013-08-29 15:42:52 -04:00
parent 1fcea5b20b
commit 082d4bd72a
1 changed files with 26 additions and 19 deletions
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45
fs/nfsd/nfs4xdr.c
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@ -1759,16 +1759,19 @@ static __be32 nfsd4_encode_components_esc(struct xdr_stream *xdr, char sep,
char esc_exit)
{
__be32 *p;
__be32 *countp;
__be32 pathlen;
int pathlen_offset;
int strlen, count=0;
char *str, *end, *next;
dprintk("nfsd4_encode_components(%s)\n", components);
pathlen_offset = xdr->buf->len;
p = xdr_reserve_space(xdr, 4);
if (!p)
return nfserr_resource;
countp = p;
WRITE32(0); /* We will fill this in with @count later */
p++; /* We will fill this in with @count later */
end = str = components;
while (*end) {
bool found_esc = false;
@ -1801,8 +1804,8 @@ static __be32 nfsd4_encode_components_esc(struct xdr_stream *xdr, char sep,
end++;
str = end;
}
p = countp;
WRITE32(count);
pathlen = htonl(xdr->buf->len - pathlen_offset);
write_bytes_to_xdr_buf(xdr->buf, pathlen_offset, &pathlen, 4);
return 0;
}
@ -2054,7 +2057,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
struct kstatfs statfs;
__be32 *p;
int starting_len = xdr->buf->len;
__be32 *attrlenp;
int attrlen_offset;
__be32 attrlen;
u32 dummy;
u64 dummy64;
u32 rdattr_err = 0;
@ -2159,10 +2163,12 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
WRITE32(1);
WRITE32(bmval0);
}
attrlen_offset = xdr->buf->len;
p = xdr_reserve_space(xdr, 4);
if (!p)
goto out_resource;
attrlenp = p++; /* to be backfilled later */
p++; /* to be backfilled later */
if (bmval0 & FATTR4_WORD0_SUPPORTED_ATTRS) {
u32 word0 = nfsd_suppattrs0(minorversion);
@ -2534,7 +2540,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
WRITE32(NFSD_SUPPATTR_EXCLCREAT_WORD2);
}
*attrlenp = htonl((char *)xdr->p - (char *)attrlenp - 4);
attrlen = htonl(xdr->buf->len - attrlen_offset - 4);
write_bytes_to_xdr_buf(xdr->buf, attrlen_offset, &attrlen, 4);
status = nfs_ok;
out:
@ -3664,15 +3671,16 @@ __be32 nfsd4_check_resp_size(struct nfsd4_compoundres *resp, u32 pad)
void
nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
{
struct xdr_stream *xdr = &resp->xdr;
struct nfs4_stateowner *so = resp->cstate.replay_owner;
struct svc_rqst *rqstp = resp->rqstp;
__be32 *statp;
int post_err_offset;
nfsd4_enc encoder;
__be32 *p;
RESERVE_SPACE(8);
WRITE32(op->opnum);
statp = p++; /* to be backfilled at the end */
post_err_offset = xdr->buf->len;
if (op->opnum == OP_ILLEGAL)
goto status;
@ -3698,20 +3706,19 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
* bug if we had to do this on a non-idempotent op:
*/
warn_on_nonidempotent_op(op);
resp->xdr.p = statp + 1;
xdr_truncate_encode(xdr, post_err_offset);
}
if (so) {
int len = xdr->buf->len - post_err_offset;
so->so_replay.rp_status = op->status;
so->so_replay.rp_buflen = (char *)resp->xdr.p
- (char *)(statp+1);
memcpy(so->so_replay.rp_buf, statp+1, so->so_replay.rp_buflen);
so->so_replay.rp_buflen = len;
read_bytes_from_xdr_buf(xdr->buf, post_err_offset,
so->so_replay.rp_buf, len);
}
status:
/*
* Note: We write the status directly, instead of using WRITE32(),
* since it is already in network byte order.
*/
*statp = op->status;
/* Note that op->status is already in network byte order: */
write_bytes_to_xdr_buf(xdr->buf, post_err_offset - 4, &op->status, 4);
}
/*