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Fix readlink(2)

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This patch addresses three issues related to symlinks.

1) Revert the zfs_follow_link() function to a modified version
of the original zfs_readlink().  The only changes from the
original OpenSolaris version relate to using Linux types.
For the moment this means no vnode's and no zfsvfs_t.  The
caller zpl_follow_link() was also updated accordingly.  This
change was reverted because it was slightly gratuitious.

2) Update zpl_follow_link() to use local variables for the
link buffer.  I'd forgotten that iov.iov_base is updated by
uiomove() so after the call to zfs_readlink() it can not longer
be used.  We need our own private copy of the link pointer.

3) Allocate MAXPATHLEN instead of MAXPATHLEN+1.  By default
MAXPATHLEN is 4096 bytes which is a full page, adding one to
it pushes it slightly over a page.  That means you'll likely
end up allocating 2 pages which is wasteful of memory and
possibly slightly slower.
This commit is contained in:
Brian Behlendorf 2011-02-16 15:54:55 -08:00
parent b9f6a49025
commit 8b4f9a2d55
2 changed files with 36 additions and 28 deletions
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33
module/zfs/zfs_vnops.c
View File

@ -3183,8 +3183,9 @@ EXPORT_SYMBOL(zfs_symlink);
* Return, in the buffer contained in the provided uio structure, * Return, in the buffer contained in the provided uio structure,
* the symbolic path referred to by ip. * the symbolic path referred to by ip.
* *
* IN: dentry - dentry of symbolic link. * IN: ip - inode of symbolic link
* nd - namedata for symlink * uio - structure to contain the link path.
* cr - credentials of caller.
* *
* RETURN: 0 if success * RETURN: 0 if success
* error code if failure * error code if failure
@ -3194,47 +3195,29 @@ EXPORT_SYMBOL(zfs_symlink);
*/ */
/* ARGSUSED */ /* ARGSUSED */
int int
zfs_follow_link(struct dentry *dentry, struct nameidata *nd) zfs_readlink(struct inode *ip, uio_t *uio, cred_t *cr)
{ {
struct inode *ip = dentry->d_inode;
znode_t *zp = ITOZ(ip); znode_t *zp = ITOZ(ip);
zfs_sb_t *zsb = ITOZSB(ip); zfs_sb_t *zsb = ITOZSB(ip);
struct iovec iov;
uio_t uio;
int error; int error;
ZFS_ENTER(zsb); ZFS_ENTER(zsb);
ZFS_VERIFY_ZP(zp); ZFS_VERIFY_ZP(zp);
iov.iov_len = MAXPATHLEN + 1;
iov.iov_base = kmem_zalloc(iov.iov_len, KM_SLEEP);
uio.uio_iov = &iov;
uio.uio_iovcnt = 1;
uio.uio_resid = iov.iov_len;
uio.uio_segflg = UIO_SYSSPACE;
mutex_enter(&zp->z_lock); mutex_enter(&zp->z_lock);
if (zp->z_is_sa) if (zp->z_is_sa)
error = sa_lookup_uio(zp->z_sa_hdl, SA_ZPL_SYMLINK(zsb), &uio); error = sa_lookup_uio(zp->z_sa_hdl,
SA_ZPL_SYMLINK(zsb), uio);
else else
error = zfs_sa_readlink(zp, &uio); error = zfs_sa_readlink(zp, uio);
mutex_exit(&zp->z_lock); mutex_exit(&zp->z_lock);
ZFS_ACCESSTIME_STAMP(zsb, zp); ZFS_ACCESSTIME_STAMP(zsb, zp);
zfs_inode_update(zp); zfs_inode_update(zp);
if (error) {
kmem_free(iov.iov_base, iov.iov_len);
nd_set_link(nd, ERR_PTR(error));
} else {
nd_set_link(nd, iov.iov_base);
}
ZFS_EXIT(zsb); ZFS_EXIT(zsb);
return (error); return (error);
} }
EXPORT_SYMBOL(zfs_follow_link); EXPORT_SYMBOL(zfs_readlink);
/* /*
* Insert a new entry into directory tdip referencing sip. * Insert a new entry into directory tdip referencing sip.

31
module/zfs/zpl_inode.c
View File

@ -245,8 +245,33 @@ out:
static void * static void *
zpl_follow_link(struct dentry *dentry, struct nameidata *nd) zpl_follow_link(struct dentry *dentry, struct nameidata *nd)
{ {
(void) zfs_follow_link(dentry, nd); struct inode *ip = dentry->d_inode;
return NULL; struct iovec iov;
uio_t uio;
char *link;
cred_t *cr;
int error;
cr = (cred_t *)get_current_cred();
iov.iov_len = MAXPATHLEN;
iov.iov_base = link = kmem_zalloc(MAXPATHLEN, KM_SLEEP);
uio.uio_iov = &iov;
uio.uio_iovcnt = 1;
uio.uio_resid = (MAXPATHLEN - 1);
uio.uio_segflg = UIO_SYSSPACE;
error = zfs_readlink(ip, &uio, cr);
if (error) {
kmem_free(link, MAXPATHLEN);
nd_set_link(nd, ERR_PTR(error));
} else {
nd_set_link(nd, link);
}
put_cred(cr);
return (NULL);
} }
static void static void
@ -256,7 +281,7 @@ zpl_put_link(struct dentry *dentry, struct nameidata *nd, void *ptr)
link = nd_get_link(nd); link = nd_get_link(nd);
if (!IS_ERR(link)) if (!IS_ERR(link))
kmem_free(link, MAXPATHLEN + 1); kmem_free(link, MAXPATHLEN);
} }
static int static int