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Allocate descriptor number in dupfdopen() itself instead of depending on

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the caller using finstall().
This saves us the filedesc lock/unlock cycle, fhold()/fdrop() cycle and closes
a race between finstall() and dupfdopen().

MFC after:	1 month
This commit is contained in:
Pawel Jakub Dawidek 2012-06-13 21:32:35 +00:00
parent 7f35af0110
commit 3812dcd3de
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=237033
3 changed files with 27 additions and 29 deletions
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34
sys/kern/kern_descrip.c
View File

@ -2588,13 +2588,13 @@ sys_flock(struct thread *td, struct flock_args *uap)
* Duplicate the specified descriptor to a free descriptor.
*/
int
dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode, int error)
dupfdopen(struct thread *td, struct filedesc *fdp, int dfd, int mode, int openerror, int *indxp)
{
struct file *wfp;
struct file *fp;
int error, indx;
KASSERT(error == ENODEV || error == ENXIO,
("unexpected error %d in %s", error, __func__));
KASSERT(openerror == ENODEV || openerror == ENXIO,
("unexpected error %d in %s", openerror, __func__));
/*
* If the to-be-dup'd fd number is greater than the allowed number
@ -2603,11 +2603,17 @@ dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode,
*/
FILEDESC_XLOCK(fdp);
if ((unsigned int)dfd >= fdp->fd_nfiles ||
(wfp = fdp->fd_ofiles[dfd]) == NULL) {
(fp = fdp->fd_ofiles[dfd]) == NULL) {
FILEDESC_XUNLOCK(fdp);
return (EBADF);
}
error = fdalloc(td, 0, &indx);
if (error != 0) {
FILEDESC_XUNLOCK(fdp);
return (error);
}
/*
* There are two cases of interest here.
*
@ -2616,26 +2622,26 @@ dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode,
* For ENXIO steal away the file structure from (dfd) and store it in
* (indx). (dfd) is effectively closed by this operation.
*/
fp = fdp->fd_ofiles[indx];
switch (error) {
switch (openerror) {
case ENODEV:
/*
* Check that the mode the file is being opened for is a
* subset of the mode of the existing descriptor.
*/
if (((mode & (FREAD|FWRITE)) | wfp->f_flag) != wfp->f_flag) {
if (((mode & (FREAD|FWRITE)) | fp->f_flag) != fp->f_flag) {
fdunused(fdp, indx);
FILEDESC_XUNLOCK(fdp);
return (EACCES);
}
fdp->fd_ofiles[indx] = wfp;
fdp->fd_ofiles[indx] = fp;
fdp->fd_ofileflags[indx] = fdp->fd_ofileflags[dfd];
fhold(wfp);
fhold(fp);
break;
case ENXIO:
/*
* Steal away the file pointer from dfd and stuff it into indx.
*/
fdp->fd_ofiles[indx] = wfp;
fdp->fd_ofiles[indx] = fp;
fdp->fd_ofiles[dfd] = NULL;
fdp->fd_ofileflags[indx] = fdp->fd_ofileflags[dfd];
fdp->fd_ofileflags[dfd] = 0;
@ -2643,11 +2649,7 @@ dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode,
break;
}
FILEDESC_XUNLOCK(fdp);
/*
* We now own the reference to fp that the ofiles[] array used to own.
* Release it.
*/
fdrop(fp, td);
*indxp = indx;
return (0);
}

18
sys/kern/vfs_syscalls.c
View File

@ -1093,7 +1093,7 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
struct file *fp;
struct vnode *vp;
int cmode;
int type, indx = -1, error, error_open;
int type, indx = -1, error;
struct flock lf;
struct nameidata nd;
int vfslocked;
@ -1143,9 +1143,7 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
goto success;
/*
* Handle special fdopen() case. bleh. dupfdopen() is
* responsible for dropping the old contents of ofiles[indx]
* if it succeeds.
* Handle special fdopen() case. bleh.
*
* Don't do this for relative (capability) lookups; we don't
* understand exactly what would happen, and we don't think
@ -1154,14 +1152,12 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
if (nd.ni_strictrelative == 0 &&
(error == ENODEV || error == ENXIO) &&
td->td_dupfd >= 0) {
/* XXX from fdopen */
error_open = error;
if ((error = finstall(td, fp, &indx, flags)) != 0)
goto bad_unlocked;
if ((error = dupfdopen(td, fdp, indx, td->td_dupfd,
flags, error_open)) == 0)
error = dupfdopen(td, fdp, td->td_dupfd, flags, error,
&indx);
if (error == 0)
goto success;
}
if (error == ERESTART)
error = EINTR;
goto bad_unlocked;
@ -4514,11 +4510,11 @@ sys_fhopen(td, uap)
VFS_UNLOCK_GIANT(vfslocked);
return (error);
}
/*
* An extra reference on `fp' has been held for us by
* falloc_noinstall().
*/
#ifdef INVARIANTS
td->td_dupfd = -1;
#endif

4
sys/sys/filedesc.h
View File

@ -109,8 +109,8 @@ struct filedesc_to_leader {
struct thread;
int closef(struct file *fp, struct thread *td);
int dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd,
int mode, int error);
int dupfdopen(struct thread *td, struct filedesc *fdp, int dfd, int mode,
int openerror, int *indxp);
int falloc(struct thread *td, struct file **resultfp, int *resultfd,
int flags);
int falloc_noinstall(struct thread *td, struct file **resultfp);