On Tue, 22 Mar 2016, J. Bruce Fields wrote:
> Possibly overkill, but I think I'll fold in something like this if you
> don't see an objection.
No objection. To answer your earlier question (does the client even send a
read if it would extend past the size returned from a recent getattr?):
Looks to me (by testing with a server that never sets eof) the answer is no.
The client won't issue reads beyond the end of the file.
Also the previous patch's subject is now a little misleading. Maybe
s/rather than/as well as/ would do.
Ben
> commit 58e18a2a14a0
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Tue Mar 22 14:08:11 2016 -0400
>
> nfsd: document read eof logic
>
> The choice of checks here is a little subtle, let's document this for
> posterity.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index 83c9abb33e8b..df0f0a86f21d 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -168,8 +168,7 @@ nfsd3_proc_read(struct svc_rqst *rqstp, struct nfsd3_readargs *argp,
> &resp->count);
> if (nfserr == 0) {
> struct inode *inode = d_inode(resp->fh.fh_dentry);
> - resp->eof = (cnt > resp->count) ||
> - ((argp->offset + resp->count) >= inode->i_size);
> + resp->eof = nfsd_eof_on_read(cnt, resp->count, argp->offset, inode->i_size);
> }
>
> RETURN_STATUS(nfserr);
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 90232bd7e498..9df898ba648f 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -3387,8 +3387,8 @@ static __be32 nfsd4_encode_splice_read(
> return nfserr;
> }
>
> - eof = (len > maxcount) ||
> - ((read->rd_offset + maxcount >= d_inode(read->rd_fhp->fh_dentry)->i_size));
> + eof = nfsd_eof_on_read(len, maxcount, read->rd_offset,
> + d_inode(read->rd_fhp->fh_dentry)->i_size);
>
> *(p++) = htonl(eof);
> *(p++) = htonl(maxcount);
> @@ -3465,8 +3465,8 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp,
> return nfserr;
> xdr_truncate_encode(xdr, starting_len + 8 + ((maxcount+3)&~3));
>
> - eof = (len > maxcount) ||
> - ((read->rd_offset + maxcount >= d_inode(read->rd_fhp->fh_dentry)->i_size));
> + eof = nfsd_eof_on_read(len, maxcount, read->rd_offset,
> + d_inode(read->rd_fhp->fh_dentry)->i_size);
>
> tmp = htonl(eof);
> write_bytes_to_xdr_buf(xdr->buf, starting_len , &tmp, 4);
> diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> index c11ba316f23f..6244e073c137 100644
> --- a/fs/nfsd/vfs.h
> +++ b/fs/nfsd/vfs.h
> @@ -139,4 +139,24 @@ static inline int nfsd_create_is_exclusive(int createmode)
> || createmode == NFS4_CREATE_EXCLUSIVE4_1;
> }
>
> +static inline bool nfsd_eof_on_read(long requested, long read,
> + loff_t offset, loff_t size)
> +{
> + /* We assume a short read means eof: */
> + if (requested > read)
> + return true;
> + /*
> + * A non-short read might also reach end of file. The spec
> + * still requires us to set eof in that case.
> + *
> + * Further operations may have modified the file size since
> + * the read, so the following check is not atomic with the read.
> + * The only case we've seen that cause a problem for a client
> + * is the case where the read returned a count of 0 without
> + * setting eof. That case was fixed by the addition of the
> + * above check.
> + */
> + return (offset + read >= size);
> +}
> +
> #endif /* LINUX_NFSD_VFS_H */
>
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