992799b91f
By decoupling synchronous drivers from VFS, we are a big step closer to
supporting driver crashes under all circumstances. That is, VFS can't
become stuck on IPC with a synchronous driver (e.g., INET) and can
recover from crashing block drivers during open/close/ioctl or during
communication with an FS.
In order to maintain serialized communication with a synchronous driver,
the communication is wrapped by a mutex on a per driver basis (not major
numbers as there can be multiple majors with identical endpoints). Majors
that share a driver endpoint point to a single mutex object.
In order to support crashes from block drivers, the file reopen tactic
had to be changed; first reopen files associated with the crashed
driver, then send the new driver endpoint to FSes. This solves a
deadlock between the FS and the block driver;
- VFS would send REQ_NEW_DRIVER to an FS, but he FS only receives it
after retrying the current request to the newly started driver.
- The block driver would refuse the retried request until all files
had been reopened.
- VFS would reopen files only after getting a reply from the initial
REQ_NEW_DRIVER.
When a character special driver crashes, all associated files have to
be marked invalid and closed (or reopened if flagged as such). However,
they can only be closed if a thread holds exclusive access to it. To
obtain exclusive access, the worker thread (which handles the new driver
endpoint event from DS) schedules a new job to garbage collect invalid
files. This way, we can signal the worker thread that was talking to the
crashed driver and will release exclusive access to a file associated
with the crashed driver and prevent the garbage collecting worker thread
from dead locking on that file.
Also, when a character special driver crashes, RS will unmap the driver
and remap it upon restart. During unmapping, associated files are marked
invalid instead of waiting for an endpoint up event from DS, as that
event might come later than new read/write/select requests and thus
cause confusion in the freshly started driver.
When locking a filp, the usage counters are no longer checked. The usage
counter can legally go down to zero during filp invalidation while there
are locks pending.
DS events are handled by a separate worker thread instead of the main
thread as reopening files could lead to another crash and a stuck thread.
An additional worker thread is then necessary to unlock it.
Finally, with everything asynchronous a race condition in do_select
surfaced. A select entry was only marked in use after succesfully sending
initial select requests to drivers and having to wait. When multiple
select() calls were handled there was opportunity that these entries
were overwritten. This had as effect that some select results were
ignored (and select() remained blocking instead if returning) or do_select
tried to access filps that were not present (because thrown away by
secondary select()). This bug manifested itself with sendrecs, but was
very hard to reproduce. However, it became awfully easy to trigger with
asynsends only.
53 lines
1.9 KiB
C
53 lines
1.9 KiB
C
#ifndef __VFS_CONST_H__
|
|
#define __VFS_CONST_H__
|
|
|
|
/* Tables sizes */
|
|
#define NR_FILPS 512 /* # slots in filp table */
|
|
#define NR_LOCKS 8 /* # slots in the file locking table */
|
|
#define NR_MNTS 16 /* # slots in mount table */
|
|
#define NR_VNODES 512 /* # slots in vnode table */
|
|
#define NR_WTHREADS 8 /* # slots in worker thread table */
|
|
|
|
#define NR_NONEDEVS NR_MNTS /* # slots in nonedev bitmap */
|
|
|
|
/* Miscellaneous constants */
|
|
#define SU_UID ((uid_t) 0) /* super_user's uid_t */
|
|
#define SYS_UID ((uid_t) 0) /* uid_t for system processes and INIT */
|
|
#define SYS_GID ((gid_t) 0) /* gid_t for system processes and INIT */
|
|
|
|
#define FP_BLOCKED_ON_NONE 0 /* not blocked */
|
|
#define FP_BLOCKED_ON_PIPE 1 /* susp'd on pipe */
|
|
#define FP_BLOCKED_ON_LOCK 2 /* susp'd on lock */
|
|
#define FP_BLOCKED_ON_POPEN 3 /* susp'd on pipe open */
|
|
#define FP_BLOCKED_ON_SELECT 4 /* susp'd on select */
|
|
#define FP_BLOCKED_ON_DOPEN 5 /* susp'd on device open */
|
|
#define FP_BLOCKED_ON_OTHER 6 /* blocked on other process, check
|
|
fp_task to find out */
|
|
|
|
/* test if the process is blocked on something */
|
|
#define fp_is_blocked(fp) ((fp)->fp_blocked_on != FP_BLOCKED_ON_NONE)
|
|
|
|
/* test if reply is a driver reply */
|
|
#define IS_DRV_REPLY(x) (IS_DEV_RS(x) || IS_BDEV_RS(x) || (x) == TASK_REPLY)
|
|
#define DUP_MASK 0100 /* mask to distinguish dup2 from dup */
|
|
|
|
#define LOOK_UP 0 /* tells search_dir to lookup string */
|
|
#define ENTER 1 /* tells search_dir to make dir entry */
|
|
#define DELETE 2 /* tells search_dir to delete entry */
|
|
#define IS_EMPTY 3 /* tells search_dir to ret. OK or ENOTEMPTY */
|
|
|
|
#define SYMLOOP 16
|
|
|
|
#define LABEL_MAX 16 /* maximum label size (including '\0'). Should
|
|
* not be smaller than 16 or bigger than
|
|
* M3_LONG_STRING.
|
|
*/
|
|
|
|
/* Args to dev_io */
|
|
#define VFS_DEV_READ 2001
|
|
#define VFS_DEV_WRITE 2002
|
|
#define VFS_DEV_IOCTL 2005
|
|
#define VFS_DEV_SELECT 2006
|
|
|
|
#endif
|