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Redesigned sys_open call

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fs0 used to receive open() requests and notify pager about them via a syscall ipc.
This caused deadlocks because normally request flow is mm0 -> fs0 on all other calls.
The solution was to have mm0 ask and validate file descriptors from fs0 on the first
request instance that involved that file descriptor. By this method we delay the
validation of the fd until its first use, and avoid deadlock. It also fits well with
the lazy request handling design philosophy.
This commit is contained in:
Bahadir Balban
2008-09-16 15:50:00 +03:00
parent 398bc0c914
commit 510852b8b8
7 changed files with 189 additions and 138 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
tasks/fs0/include/syscalls.h
View File

@@ -13,6 +13,8 @@ int sys_mkdir(l4id_t sender, const char *pathname, unsigned int mode);
int sys_chdir(l4id_t sender, const char *pathname);
/* Calls from pager that completes a posix call */
int pager_sys_open(l4id_t sender, l4id_t opener, int fd);
int pager_sys_read(l4id_t sender, unsigned long vnum, unsigned long f_offset,
unsigned long npages, void *pagebuf);

3
tasks/fs0/main.c
View File

@@ -88,6 +88,9 @@ void handle_fs_requests(void)
pager_sys_read(sender, (unsigned long)mr[0], (unsigned long)mr[1],
(unsigned long)mr[2], (void *)mr[3]);
break;
case L4_IPC_TAG_PAGER_OPEN:
pager_sys_open(sender, (l4id_t)mr[0], (int)mr[1]);
break;
case L4_IPC_TAG_PAGER_WRITE:
pager_sys_write(sender, (unsigned long)mr[0], (unsigned long)mr[1],
(unsigned long)mr[2], (void *)mr[3]);

65
tasks/fs0/src/syscalls.c
View File

@@ -18,39 +18,50 @@
#include <alloca.h>
#include <path.h>
#define NILFD -1
/*
* This notifies mm0 that this is the fd that refers to this vnode number
* from now on. Note this is a one-way call.
* This informs mm0 about an opened file descriptors.
*
* MM0 *also* keeps track of fd's because mm0 is a better candidate
* for handling syscalls that access file content (i.e. read/write) since
* it maintains the page cache.
* it maintains the page cache. MM0 is not notified about opened files
* but is rather informed when it asks to be. This avoids deadlocks by
* keeping the request flow in one way.
*/
int pager_sys_open(l4id_t sender, int fd, unsigned long vnum, unsigned long size)
int pager_sys_open(l4id_t sender, l4id_t opener, int fd)
{
int err;
struct tcb *task;
struct vnode *v;
printf("%s/%s\n", __TASKNAME__, __FUNCTION__);
l4_save_ipcregs();
write_mr(L4SYS_ARG0, sender);
write_mr(L4SYS_ARG1, fd);
write_mr(L4SYS_ARG2, vnum);
write_mr(L4SYS_ARG3, size);
/* Tell pager about open request. Check ipc error. */
if ((err = l4_sendrecv(PAGER_TID, PAGER_TID, L4_IPC_TAG_PAGER_OPEN)) < 0) {
printf("%s: L4 IPC Error: %d.\n", __FUNCTION__, err);
return err;
/* Check if such task exists */
if (!(task = find_task(opener))) {
l4_ipc_return(-ESRCH);
return 0;
}
/* Check if syscall itself was successful */
if ((err = l4_get_retval()) < 0) {
printf("%s: Pager open Error: %d.\n", __FUNCTION__, fd);
return err;
/* Check if that fd has been opened */
if (task->fd[fd] == NILFD) {
l4_ipc_return(-EBADF);
return 0;
}
l4_restore_ipcregs();
/* Search the vnode by that vnum */
if (IS_ERR(v = vfs_lookup_byvnum(vfs_root.pivot->sb,
task->fd[fd]))) {
l4_ipc_return((int)v);
return 0;
}
/* Write file information */
write_mr(L4SYS_ARG0, v->vnum);
write_mr(L4SYS_ARG1, v->size);
/* Return ipc with success code */
l4_ipc_return(0);
return 0;
}
@@ -99,7 +110,7 @@ struct vnode *vfs_create(struct tcb *task, struct pathdata *pdata,
* Pager notifies vfs about a closed file descriptor.
*
* FIXME: fsync + close could be done under a single "close" ipc
* from pager. Currently there are 2 ipcs: 1 fsync + 1 fd close.
* from pager. Currently there are 2 ipcs: 1 fsync + 1 fd close.
*/
int pager_sys_close(l4id_t sender, l4id_t closer, int fd)
{
@@ -116,7 +127,7 @@ int pager_sys_close(l4id_t sender, l4id_t closer, int fd)
l4_ipc_return(err);
return 0;
}
task->fd[fd] = -1;
task->fd[fd] = NILFD;
l4_ipc_return(0);
return 0;
@@ -133,7 +144,7 @@ int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
struct vnode *v;
struct tcb *task;
int fd;
int retval, err;
int retval;
// printf("%s/%s\n", __TASKNAME__, __FUNCTION__);
@@ -171,12 +182,6 @@ int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
/* Assign the new fd with the vnode's number */
task->fd[fd] = v->vnum;
/* Tell the pager about opened vnode information */
if ((err = pager_sys_open(sender, fd, v->vnum, v->size)) < 0) {
retval = err;
goto out;
}
out:
pathdata_destroy(pdata);
l4_ipc_return(retval);