Because pipes have no file position. VFS maintained (file) offsets into a
buffer internal to PFS and stored them in vnodes for simplicity, mixing
the responsibilities of filp and vnode objects.
With this patch PFS ignores the position field in REQ_READ and REQ_WRITE
requests making VFS' job a lot simpler.
.sync and fsync used unnecessarily restrictive locking type
.fsync violated locking order by obtaining a vmnt lock after a filp lock
.fsync contained a TOCTOU bug
.new_node violated locking rules (didn't upgrade lock upon file creation)
.do_pipe used unnecessarily restrictive locking type
.always lock pipes exclusively; even a read operation might require to do
a write on a vnode object (update pipe size)
.when opening a file with O_TRUNC, upgrade vnode lock when truncating
.utime used unnecessarily restrictive locking type
.path parsing:
.always acquire VMNT_WRITE or VMNT_EXCL on vmnt and downgrade to
VMNT_READ if that was what was actually requested. This prevents the
following deadlock scenario:
thread A:
lock_vmnt(vmp, TLL_READSER);
lock_vnode(vp, TLL_READSER);
upgrade_vmnt_lock(vmp, TLL_WRITE);
thread B:
lock_vmnt(vmp, TLL_READ);
lock_vnode(vp, TLL_READSER);
thread A will be stuck in upgrade_vmnt_lock and thread B is stuck in
lock_vnode. This happens when, for example, thread A tries create a
new node (open.c:new_node) and thread B tries to do eat_path to
change dir (stadir.c:do_chdir). When the path is being resolved, a
vnode is always locked with VNODE_OPCL (TLL_READSER) and then
downgraded to VNODE_READ if read-only is actually requested. Thread
A locks the vmnt with VMNT_WRITE (TLL_READSER) which still allows
VMNT_READ locks. Thread B can't acquire a lock on the vnode because
thread A has it; Thread A can't upgrade its vmnt lock to VMNT_WRITE
(TLL_WRITE) because thread B has a VMNT_READ lock on it.
By serializing vmnt locks during path parsing, thread B can only
acquire a lock on vmp when thread A has completely finished its
operation.
By making m_in job local (i.e., each job has its own copy of m_in instead
of refering to the global m_in) we don't have to store and restore m_in
on every thread yield. This reduces overhead. Moreover, remove the
assumption that m_in is preserved. Do_XXX functions have to copy the
system call parameters as soon as possible and only pass those copies to
other functions.
Furthermore, this patch cleans up some code and uses better types in a lot
of places.
- Fix locking bug when unable to send DEV_SELECT request. Upon failure
VFS tried to cancel the select operation, but this failed due to trying
to lock a filp that was already locked to send the request in the first
place. Do_select_request now handles locking of filps itself instead of
relying on the caller to do it. This fixes a crash when killing INET.
- Fix failure to revive a process after a non-blocking select operation
yielded no ready select operations when replying DEV_SEL_REPL1.
- Improve readability by using OK, SUSPEND, and standard error values as
results instead of having separate macros in select.
- Don't print not having a driver for a major device; after killing a driver
select will trigger this printf.
- Remove redundant code.
- Always wait for the initial reply from an asynchronous select request,
even if the select has been satisfied on another file descriptor or
was canceled due to a serious error.
- Restart asynchronous selects if upon reply from the driver turns out
that there are deferred operations (and do not forget we're still
interested in the results of the deferred operations).
- Do not hang a non-blocking select when another blocking select on
the same filp is still blocking.
- Split blocking operations in read, write, and exceptions (i.e.,
blocking on read does not imply the write will block as well).
- Some loops would iterate over OPEN_MAX file descriptors instead of
the "highest" file descriptor.
- Use proper internal error return values.
- A secondary reply from a synchronous driver is essentially the same
as from an asynchronous driver (the only difference being how the
answer is received). Merge.
- Return proper error code after a driver failure.
- Auto-detect whether a driver is synchronous or asynchronous.
- Remove some code duplication.
- Clean up code (coding style, add missing comments, put all select
related code together).
Before safecopies, the IO_ENDPT and DL_ENDPT message fields were needed
to know which actual process to copy data from/to, as that process may
not always be the caller. Now that we have full safecopy support, these
fields have become useless for that purpose: the owner of the grant is
*always* the caller. Allowing the caller to supply another endpoint is
in fact dangerous, because the callee may then end up using a grant
from a third party. One could call this a variant of the confused
deputy problem.
From now on, safecopy calls should always use the caller's endpoint as
grant owner. This fully obsoletes the DL_ENDPT field in the
inet/ethernet protocol. IO_ENDPT has other uses besides identifying the
grant owner though. This patch renames IO_ENDPT to USER_ENDPT, not only
because that is a more fitting name (it should never be used for I/O
after all), but also in order to intentionally break any old system
source code outside the base system. If this patch breaks your code,
fixing it is fairly simple:
- DL_ENDPT should be replaced with m_source;
- IO_ENDPT should be replaced with m_source when used for safecopies;
- IO_ENDPT should be replaced with USER_ENDPT for any other use, e.g.
when setting REP_ENDPT, matching requests in CANCEL calls, getting
DEV_SELECT flags, and retrieving of the real user process's endpoint
in DEV_OPEN.
The changes in this patch are binary backward compatible.
this change
- makes panic() variadic, doing full printf() formatting -
no more NO_NUM, and no more separate printf() statements
needed to print extra info (or something in hex) before panicing
- unifies panic() - same panic() name and usage for everyone -
vm, kernel and rest have different names/syntax currently
in order to implement their own luxuries, but no longer
- throws out the 1st argument, to make source less noisy.
the panic() in syslib retrieves the server name from the kernel
so it should be clear enough who is panicing; e.g.
panic("sigaction failed: %d", errno);
looks like:
at_wini(73130): panic: sigaction failed: 0
syslib:panic.c: stacktrace: 0x74dc 0x2025 0x100a
- throws out report() - printf() is more convenient and powerful
- harmonizes/fixes the use of panic() - there were a few places
that used printf-style formatting (didn't work) and newlines
(messes up the formatting) in panic()
- throws out a few per-server panic() functions
- cleans up a tie-in of tty with panic()
merging printf() and panic() statements to be done incrementally.
- Revise VFS-FS protocol and update VFS/MFS/ISOFS accordingly.
- Clean up MFS by removing old, dead code (backwards compatibility is broken by
the new VFS-FS protocol, anyway) and rewrite other parts. Also, make sure all
functions have proper banners and prototypes.
- VFS should always provide a (syntactically) valid path to the FS; no need for
the FS to do sanity checks when leaving/entering mount points.
- Fix several bugs in MFS:
- Several path lookup bugs in MFS.
- A link can be too big for the path buffer.
- A mountpoint can become inaccessible when the creation of a new inode
fails, because the inode already exists and is a mountpoint.
- Introduce support for supplemental groups.
- Add test 46 to test supplemental group functionality (and removed obsolete
suppl. tests from test 2).
- Clean up VFS (not everything is done yet).
- ISOFS now opens device read-only. This makes the -r flag in the mount command
unnecessary (but will still report to be mounted read-write).
- Introduce PipeFS. PipeFS is a new FS that handles all anonymous and
named pipes. However, named pipes still reside on the (M)FS, as they are part
of the file system on disk. To make this work VFS now has a concept of
'mapped' inodes, which causes read, write, truncate and stat requests to be
redirected to the mapped FS, and all other requests to the original FS.
- all macros in consts.h that depend on NR_TASKS replaced by a FP_BLOCKED_ON_*
- fp_suspended removed and replaced by fp_blocked_on. Testing whether a process
is supended is qeual to testing whether fp_blocked_on is FP_BLOCKED_ON_NONE or
not
- fp_task is valid only if fp_blocked_on == FP_BLOCKED_ON_OTHER
- no need of special values that do not colide with valid and special endpoints
since they are not used as endpoints anymore
- suspend only takes FP_BLOCKED_ON_* values not endpoints anymore
- suspend(task) replaced by wait_for(task) which sets fp_task so we remember who
are we waiting for and suspend sets fp_blocked_on to FP_BLOCKED_ON_OTHER to
signal that we are waiting for some other process
- some functions should take endpoint_t instead of int, fixed
- When one does a select on a file descriptor that is meaningless for that particular file type, select shall indicate that the file descriptor is ready for that particular operation and that the file descriptor has no exceptional condition pending.
if the process was REVIVING. (susp_count doesn't count those
processes.) this together with dev_io SELECT suspend side effect
for asynch. character devices solves the hanging pipe bug. or
at last vastly improves it.
added sanity checks, turned off by default.
made the {NOT_,}{SUSPENDING,REVIVING} constants weirder to
help sanity checking.
