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nfsd: allow filesystems to opt out of subtree checking 

When we start allowing NFS to be reexported, then we have some problems
when it comes to subtree checking. In principle, we could allow it, but
it would mean encoding parent info in the filehandles and there may not
be enough space for that in a NFSv3 filehandle.

To enforce this at export upcall time, we add a new export_ops flag
that declares the filesystem ineligible for subtree checking.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Lance Shelton <lance.shelton@hammerspace.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Jeff Layton 2020-11-30 17:03:15 -05:00 committed by Chuck Lever
parent daab110e47
commit ba5e8187c5
4 changed files with 20 additions and 1 deletions
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12
Documentation/filesystems/nfs/exporting.rst
View File

@ -190,3 +190,15 @@ following flags are defined:
this on filesystems that have an expensive ->getattr inode operation,
or when atomicity between pre and post operation attribute collection
is impossible to guarantee.
EXPORT_OP_NOSUBTREECHK - disallow subtree checking on this fs
Many NFS operations deal with filehandles, which the server must then
vet to ensure that they live inside of an exported tree. When the
export consists of an entire filesystem, this is trivial. nfsd can just
ensure that the filehandle live on the filesystem. When only part of a
filesystem is exported however, then nfsd must walk the ancestors of the
inode to ensure that it's within an exported subtree. This is an
expensive operation and not all filesystems can support it properly.
This flag exempts the filesystem from subtree checking and causes
exportfs to get back an error if it tries to enable subtree checking
on it.

2
fs/nfs/export.c
View File

@ -171,5 +171,5 @@ const struct export_operations nfs_export_ops = {
.encode_fh = nfs_encode_fh,
.fh_to_dentry = nfs_fh_to_dentry,
.get_parent = nfs_get_parent,
.flags = EXPORT_OP_NOWCC,
.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK,
};

6
fs/nfsd/export.c
View File

@ -408,6 +408,12 @@ static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
return -EINVAL;
}
if (inode->i_sb->s_export_op->flags & EXPORT_OP_NOSUBTREECHK &&
!(*flags & NFSEXP_NOSUBTREECHECK)) {
dprintk("%s: %s does not support subtree checking!\n",
__func__, inode->i_sb->s_type->name);
return -EINVAL;
}
return 0;
}

1
include/linux/exportfs.h
View File

@ -214,6 +214,7 @@ struct export_operations {
int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
int nr_iomaps, struct iattr *iattr);
#define EXPORT_OP_NOWCC (0x1) /* Don't collect wcc data for NFSv3 replies */
#define EXPORT_OP_NOSUBTREECHK (0x2) /* Subtree checking is not supported! */
unsigned long flags;
};