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.
50 lines
1.8 KiB
C
50 lines
1.8 KiB
C
#ifndef __VFS_FILE_H__
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#define __VFS_FILE_H__
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/* This is the filp table. It is an intermediary between file descriptors and
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* inodes. A slot is free if filp_count == 0.
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*/
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EXTERN struct filp {
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mode_t filp_mode; /* RW bits, telling how file is opened */
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int filp_flags; /* flags from open and fcntl */
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int filp_state; /* state for crash recovery */
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int filp_count; /* how many file descriptors share this slot?*/
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struct vnode *filp_vno; /* vnode belonging to this file */
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u64_t filp_pos; /* file position */
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mutex_t filp_lock; /* lock to gain exclusive access */
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struct fproc *filp_softlock; /* if not NULL; this filp didn't lock the
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* vnode. Another filp already holds a lock
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* for this thread */
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/* the following fields are for select() and are owned by the generic
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* select() code (i.e., fd-type-specific select() code can't touch these).
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*/
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int filp_selectors; /* select()ing processes blocking on this fd */
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int filp_select_ops; /* interested in these SEL_* operations */
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int filp_select_flags; /* Select flags for the filp */
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/* following are for fd-type-specific select() */
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int filp_pipe_select_ops;
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} filp[NR_FILPS];
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#define FILP_CLOSED 0 /* filp_mode: associated device closed */
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#define FS_NORMAL 000 /* file descriptor can be used normally */
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#define FS_NEEDS_REOPEN 001 /* file descriptor needs to be re-opened */
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#define FS_INVALIDATED 002 /* file was invalidated */
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#define FSF_UPDATE 001 /* The driver should be informed about new
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* state.
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*/
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#define FSF_BUSY 002 /* Select operation sent to driver but no
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* reply yet.
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*/
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#define FSF_RD_BLOCK 010 /* Read request is blocking, the driver should
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* keep state.
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*/
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#define FSF_WR_BLOCK 020 /* Write request is blocking */
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#define FSF_ERR_BLOCK 040 /* Exception request is blocking */
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#define FSF_BLOCKED 070
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#endif
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