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* Have m_pulldown() use the new M_WRITABLE() macro in order to determine

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whether the given ext_buf is shared.

* Have the sf_bufs be setup with the mbuf subsystem using MEXTADD() with the
two new arguments.

Note: m_pulldown() is somewhat crotchy; the added comment explains the
situation.

Reviewed by: jlemon
This commit is contained in:
bmilekic 2000-11-11 23:04:15 +00:00
parent 3d05ea1832
commit 4ddcfae4ca
2 changed files with 33 additions and 15 deletions
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45
sys/kern/uipc_mbuf2.c
View File

@ -81,7 +81,7 @@
*
* on error return (NULL return value), original "m" will be freed.
*
* XXX M_TRAILINGSPACE/M_LEADINGSPACE on shared cluster (sharedcluster)
* XXX: M_TRAILINGSPACE/M_LEADINGSPACE only permitted on writable ext_buf.
*/
struct mbuf *
m_pulldown(m, off, len, offp)
@ -91,7 +91,7 @@ m_pulldown(m, off, len, offp)
{
struct mbuf *n, *o;
int hlen, tlen, olen;
int sharedcluster;
int writable;
/* check invalid arguments. */
if (m == NULL)
@ -176,25 +176,42 @@ m_pulldown(m, off, len, offp)
* easy cases first.
* we need to use m_copydata() to get data from <n->m_next, 0>.
*/
if ((n->m_flags & M_EXT) == 0)
sharedcluster = 0;
else {
if (n->m_ext.ext_free)
sharedcluster = 1;
else if (MEXT_IS_REF(n))
sharedcluster = 1;
else
sharedcluster = 0;
}
/*
* XXX: This code is flawed because it considers a "writable" mbuf
* data region to require all of the following:
* (i) mbuf _has_ to have M_EXT set; if it is just a regular
* mbuf, it is still not considered "writable."
* (ii) since mbuf has M_EXT, the ext_type _has_ to be
* EXT_CLUSTER. Anything else makes it non-writable.
* (iii) M_WRITABLE() must evaluate true.
* Ideally, the requirement should only be (iii).
*
* If we're writable, we're sure we're writable, because the ref. count
* cannot increase from 1, as that would require posession of mbuf
* n by someone else (which is impossible). However, if we're _not_
* writable, we may eventually become writable )if the ref. count drops
* to 1), but we'll fail to notice it unless we re-evaluate
* M_WRITABLE(). For now, we only evaluate once at the beginning and
* live with this.
*/
/*
* XXX: This is dumb. If we're just a regular mbuf with no M_EXT,
* then we're not "writable," according to this code.
*/
writable = 0;
if ((n->m_flags & M_EXT) && (n->m_ext.ext_type == EXT_CLUSTER) &&
M_WRITABLE(n))
writable = 1;
if ((off == 0 || offp) && M_TRAILINGSPACE(n) >= tlen
&& !sharedcluster) {
&& writable) {
m_copydata(n->m_next, 0, tlen, mtod(n, caddr_t) + n->m_len);
n->m_len += tlen;
m_adj(n->m_next, tlen);
goto ok;
}
if ((off == 0 || offp) && M_LEADINGSPACE(n->m_next) >= hlen
&& !sharedcluster) {
&& writable) {
n->m_next->m_data -= hlen;
n->m_next->m_len += hlen;
bcopy(mtod(n, caddr_t) + off, mtod(n->m_next, caddr_t), hlen);

3
sys/kern/uipc_syscalls.c
View File

@ -1625,7 +1625,8 @@ sendfile(struct proc *p, struct sendfile_args *uap)
/*
* Setup external storage for mbuf.
*/
MEXTADD(m, sf->kva, PAGE_SIZE, sf_buf_free, NULL);
MEXTADD(m, sf->kva, PAGE_SIZE, sf_buf_free, NULL, M_RDONLY,
EXT_SFBUF);
m->m_data = (char *) sf->kva + pgoff;
m->m_pkthdr.len = m->m_len = xfsize;
/*