Date: Wed, 27 Mar 2013 18:37:51 -0700 From: mdf@FreeBSD.org To: freebsd-current@freebsd.org, freebsd-fs@freebsd.org Subject: [RFC] use a shared lock for VOP_GETEXTATTR Message-ID: <CAMBSHm9VgD9Pcmiap3Cy1eW8GD9k06q%2BsCzaSJ%2B_wyA6ZFioTA@mail.gmail.com> In-Reply-To: <CAMBSHm8Akz2-tUhjYm9%2BH3YTN31N8=OhGHX1ZpdV4-VixFQm%2BQ@mail.gmail.com> References: <CAMBSHm8Akz2-tUhjYm9%2BH3YTN31N8=OhGHX1ZpdV4-VixFQm%2BQ@mail.gmail.com>
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[-- Attachment #1 --]
VOP_GETEXTATTR is currently called with an exclusive lock, which seems
like overkill for what is essentially a read operation. I had a look
over the various in-tree filesystems and it didn't look like any of
them will have a problem if a shared-mode lock is used for
vop_getextattr.
Does anyone know otherwise? Is someone using extended attributes
regularly who can test this?
[sorry if this is a duplicate; I first sent from my non-FreeBSD mail]
Thanks,
matthew
[-- Attachment #2 --]
From aa6d6c716bd19ce32e3b908727fbda65d345b7ab Mon Sep 17 00:00:00 2001
From: Matthew Fleming <mdf@FreeBSD.org>
Date: Wed, 27 Mar 2013 18:23:17 -0700
Subject: [PATCH] Use a shared lock for VOP_GETEXTATTR, as it is a read-like operation.
MFC after: 1 week
---
sys/kern/vfs_extattr.c | 2 +-
sys/kern/vfs_vnops.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/sys/kern/vfs_extattr.c b/sys/kern/vfs_extattr.c
index 85fc839..700a70c 100644
--- a/sys/kern/vfs_extattr.c
+++ b/sys/kern/vfs_extattr.c
@@ -321,17 +321,17 @@ extattr_get_vp(struct vnode *vp, int attrnamespace, const char *attrname,
void *data, size_t nbytes, struct thread *td)
{
struct uio auio, *auiop;
struct iovec aiov;
ssize_t cnt;
size_t size, *sizep;
int error;
- vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+ vn_lock(vp, LK_SHARED | LK_RETRY);
/*
* Slightly unusual semantics: if the user provides a NULL data
* pointer, they don't want to receive the data, just the maximum
* read length.
*/
auiop = NULL;
sizep = NULL;
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index c8f832f..6849730 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -1753,17 +1753,17 @@ vn_extattr_get(struct vnode *vp, int ioflg, int attrnamespace,
auio.uio_iovcnt = 1;
auio.uio_rw = UIO_READ;
auio.uio_segflg = UIO_SYSSPACE;
auio.uio_td = td;
auio.uio_offset = 0;
auio.uio_resid = *buflen;
if ((ioflg & IO_NODELOCKED) == 0)
- vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+ vn_lock(vp, LK_SHARED | LK_RETRY);
ASSERT_VOP_LOCKED(vp, "IO_NODELOCKED with no vp lock held");
/* authorize attribute retrieval as kernel */
error = VOP_GETEXTATTR(vp, attrnamespace, attrname, &auio, NULL, NULL,
td);
if ((ioflg & IO_NODELOCKED) == 0)
--
1.7.3.2
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