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Add a new kind of reference count (fd_holdcnt) to struct filedesc

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which holds on to just the data structure and the mutex.  (The
existing refcount (fd_refcnt) holds onto the open files in the
descriptor.)

The fd_holdcnt is protected by fdesc_mtx, fd_refcnt by FILEDESC_LOCK.

Add fdhold(struct proc *) which gets a hold on the filedescriptors of
the specified proc..

Add fddrop(struct filedesc *) which drops the fd_holdcnt and if zero
destroys the mutex and frees the memory.

Initialize the fd_holdcnt to one in fdinit().  Normal operations on
the filedesc structure will not change it.

In fdfree() use fddrop() to dispose of the mutex and structure.  Hold
the FILEDESC_LOCK() until we have cleaned out the contents and carefully
set the fields to null values during cleanup.

Use fdhold()/fddrop() in mountcheckdirs() and sysctl_kern_file().
This commit is contained in:
Poul-Henning Kamp 2004-12-14 09:09:51 +00:00
parent 7e727eadc4
commit d986dbb448
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=138838
2 changed files with 47 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
sys/kern/kern_descrip.c
View File

@ -1394,6 +1394,7 @@ fdinit(struct filedesc *fdp)
/* Create the file descriptor table. */
newfdp->fd_fd.fd_refcnt = 1;
newfdp->fd_fd.fd_holdcnt = 1;
newfdp->fd_fd.fd_cmask = CMASK;
newfdp->fd_fd.fd_ofiles = newfdp->fd_dfiles;
newfdp->fd_fd.fd_ofileflags = newfdp->fd_dfileflags;
@ -1402,6 +1403,34 @@ fdinit(struct filedesc *fdp)
return (&newfdp->fd_fd);
}
static struct filedesc *
fdhold(struct proc *p)
{
struct filedesc *fdp;
mtx_lock(&fdesc_mtx);
fdp = p->p_fd;
if (fdp != NULL)
fdp->fd_holdcnt++;
mtx_unlock(&fdesc_mtx);
return (fdp);
}
static void
fddrop(struct filedesc *fdp)
{
int i;
mtx_lock(&fdesc_mtx);
i = --fdp->fd_holdcnt;
mtx_unlock(&fdesc_mtx);
if (i > 0)
return;
mtx_destroy(&fdp->fd_mtx);
FREE(fdp, M_FILEDESC);
}
/*
* Share a filedesc structure.
*/
@ -1588,7 +1617,6 @@ fdfree(struct thread *td)
* We are the last reference to the structure, so we can
* safely assume it will not change out from under us.
*/
FILEDESC_UNLOCK(fdp);
fpp = fdp->fd_ofiles;
for (i = fdp->fd_lastfile; i-- >= 0; fpp++) {
if (*fpp)
@ -1604,14 +1632,22 @@ fdfree(struct thread *td)
FREE(fdp->fd_ofiles, M_FILEDESC);
if (NDSLOTS(fdp->fd_nfiles) > NDSLOTS(NDFILE))
FREE(fdp->fd_map, M_FILEDESC);
fdp->fd_nfiles = 0;
if (fdp->fd_cdir)
vrele(fdp->fd_cdir);
fdp->fd_cdir = NULL;
if (fdp->fd_rdir)
vrele(fdp->fd_rdir);
fdp->fd_rdir = NULL;
if (fdp->fd_jdir)
vrele(fdp->fd_jdir);
mtx_destroy(&fdp->fd_mtx);
FREE(fdp, M_FILEDESC);
fdp->fd_jdir = NULL;
FILEDESC_UNLOCK(fdp);
fddrop(fdp);
}
/*
@ -2262,8 +2298,7 @@ dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode,
* mount point.
*/
void
mountcheckdirs(olddp, newdp)
struct vnode *olddp, *newdp;
mountcheckdirs(struct vnode *olddp, struct vnode *newdp)
{
struct filedesc *fdp;
struct proc *p;
@ -2273,12 +2308,9 @@ mountcheckdirs(olddp, newdp)
return;
sx_slock(&allproc_lock);
LIST_FOREACH(p, &allproc, p_list) {
mtx_lock(&fdesc_mtx);
fdp = p->p_fd;
if (fdp == NULL) {
mtx_unlock(&fdesc_mtx);
fdp = fdhold(p);
if (fdp == NULL)
continue;
}
nrele = 0;
FILEDESC_LOCK_FAST(fdp);
if (fdp->fd_cdir == olddp) {
@ -2292,7 +2324,6 @@ mountcheckdirs(olddp, newdp)
nrele++;
}
FILEDESC_UNLOCK_FAST(fdp);
mtx_unlock(&fdesc_mtx);
while (nrele--)
vrele(olddp);
}
@ -2383,11 +2414,9 @@ sysctl_kern_file(SYSCTL_HANDLER_ARGS)
xf.xf_pid = p->p_pid;
xf.xf_uid = p->p_ucred->cr_uid;
PROC_UNLOCK(p);
mtx_lock(&fdesc_mtx);
if ((fdp = p->p_fd) == NULL) {
mtx_unlock(&fdesc_mtx);
fdp = fdhold(p);
if (fdp == NULL)
continue;
}
FILEDESC_LOCK_FAST(fdp);
for (n = 0; n < fdp->fd_nfiles; ++n) {
if ((fp = fdp->fd_ofiles[n]) == NULL)
@ -2406,7 +2435,7 @@ sysctl_kern_file(SYSCTL_HANDLER_ARGS)
break;
}
FILEDESC_UNLOCK_FAST(fdp);
mtx_unlock(&fdesc_mtx);
fddrop(fdp);
if (error)
break;
}

3
sys/sys/filedesc.h
View File

@ -58,7 +58,8 @@ struct filedesc {
int fd_lastfile; /* high-water mark of fd_ofiles */
int fd_freefile; /* approx. next free file */
u_short fd_cmask; /* mask for file creation */
u_short fd_refcnt; /* reference count */
u_short fd_refcnt; /* thread reference count */
u_short fd_holdcnt; /* hold count on structure + mutex */
struct mtx fd_mtx; /* protects members of this struct */
int fd_locked; /* long lock flag */