Current patches

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| ### Current patches The purpose of this page is to keep people better informed about ongoing work between UML releases by making the patches currently in my working pool visible to the public. This should alleviate several issues with UML development: Not infrequently, someone finds a bug in UML, chases it down, and submits a patch, not knowing that the bug has already been fixed in my tree. Since my working tree isn't public until a release, there was no way for anyone to know that the bug was already fixed. Also not infrequently, the fixes in my tree are incomplete or wrong in some other way. Having those patches available before the release gives UML developers a way to test and sanity-check the patches before they are released to the public. Having the patches in a release split out makes it easier to fix new bugs by allowing users to back out patches until the bug disappears. Then we know which patch was responsible and can probably figure out the problem quickly. This also allows non-expert users to help track things down since the only expertise needed is the ability to run patch and build UML from source. To this end, I've started using quilt to manage patches, and will publish the unreleased patches in my current tree here. It will be updated frequently so that there will only be a short window between me putting a patch in my tree and it appearing here. So, here are the patches pending in my 2.4 and 2.6 trees. The version is the last public release of UML to which these are applied. They apply in order.
2.4.27-3um
> Patches tarball : last modified - Wed Apr 26 17:56:03 EDT 2006
> notes
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This removes some useless ioctls from the ubd driver.
> ifup-flush
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From Gerd Knorr - this avoids a network deadlock that can happen when the host side of an interface is full when the UML interface is brought up. In this case, SIGIOs will never be delivered since no new data is ever queued to the host side.
> build-cleanups
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> Keeping 2.4 in sync with 2.6 - this moves the linker scripts and main.c from arch/um to arch/um/kernel.
> sysemu
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This is Blaisorblade's sysemu patch for UML, cleaned up some, and with support added for tt mode. This adds support to UML for Laurent Vivier's context-switch-reducing sysemu patch.
> crypto
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This pulls the crypto stuff into the UML config.
> scheduler
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This fixes a use-after-free bug in the context switching. A process going out of context after exiting wakes up the next process and then kills itself. The problem is that when it gets around to killing itself is up to the host and can happen a long time later, including after the incoming process has freed its stack, and that memory is possibly being used for something else. The fix is to have the incoming process kill the exiting process just to make sure it can't be running at the point that its stack is freed.
> eintr
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> Add some more EINTR safety with some more uses of CATCH_EINTR. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> no-mo-ghash
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This removes the much-hated ghash.h. physmem now makes do with an rbtree instead.
> need-bash
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This forces make to use bash rather than whatever /bin/sh is linked to. There are some bash extensions used in the build (and maybe this needs fixing) and when /bin/sh isn't bash, then the build fails mysteriously.
> skas-flush-tlb
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> Do not flush the whole kernel page table instead of flushing only a range in SKAS mode: loop from start to end instead than to start_vm to end_vm. To test a lot, since it could well be wrong, or some callers could be passing wrong parameters (they were ignored!). Anyway, it seems that this is safe and that most callers are in arch-independent code (i.e. correct one). But actually I did not test modules well. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it> I eyeballed all the callers, and they seem to be doing the right thing - jdike
> tmp-exec
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This adds a check that /tmp is not mounted noexec. UML needs to be able to do PROT_EXEC mmaps of temp files. Previously, a noexec /tmp would cause an early mysterious UML crash.
> 2.4.27
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> This is the update to 2.4.27. Upgrading to 2.4.27 is probably better done by applying uml-patch-2.4.27-1.
> no-unit-at-a-time
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> Avoid that gcc breaks UML with "unit at a time" compilation mode. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> move-hostfs
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> To make patch backports from 2.6 easier, this patch moves hostfs to fs, where it is in 2.6, from arch/um/fs.
> kill-warnings
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> Fixes some little warnings about "Defined but not used ..." by #ifdef'ing things Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> tkill
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> Avoids compile failure when host misses tkill(), by simply using kill() in that case. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> disable-sysemu
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> Adds the "nosysemu" command line parameter to disable SYSEMU Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> proc-sysemu
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> Adds /proc/sysemu to toggle SYSEMU usage. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
> sysemu-fixes
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> From: <blaisorblade_spam@yahoo.it> - Correct some silly errors (dereferencing a pointer before checking if it's != NULL when creating /proc/sysemu, some error messages) - separate using_sysemu from sysemu_supported (so to refuse to activate sysemu if it is not supported, avoiding panics) - not probe sysemu if in tt mode. Signed-off-by: <blaisorblade_spam@yahoo.it>
> stack-overflow
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
> Remove the stack overflow check in the page fault handler, which was just wrong, and could be triggered by a process.
> bh-update
> Last Changed - Thu Oct 13 18:19:23 EDT 2005
2.6.17-rc2
> Patches tarball : last modified - Wed Apr 26 17:56:03 EDT 2006
> fix-iomem
> Last Changed - Thu Apr 13 13:25:07 EDT 2006
> From "Victor V. Vengerov" <Victor.Vengerov@oktetlabs.ru> We need to walk the region list properly.
> jmpbuf
> Last Changed - Tue Mar 21 11:55:01 EST 2006
> Newer libcs don't define the JB_* jmp_buf access macros. If this is the case, we provide values ourselves.
> devshm
> Last Changed - Tue Apr 25 12:00:07 EDT 2006
> UML really wants shared memory semantics form its physical memory map file, and the place for that is /dev/shm. So move the default, and fix the error messages to recognize that this value can be overridden. Signed-off-by: Rob Landley <rob@landley.net>
> fix-ubd-lock1
> Last Changed - Mon Apr 3 08:54:12 EDT 2006
> I noticed ubd_lock being used to protect crazy amounts of code. This patch gets rid of the worst offenders.
> punctuation-fixes
> Last Changed - Tue Mar 21 11:56:32 EST 2006
> I'm inconsistent enough about using dashes or underscores for punctuation within filenames. However, sometimes I use both within the same name, and I got sick of this. So, this fixes those cases.
> ubd-release-akpm
> Last Changed - Mon Apr 3 08:55:44 EDT 2006
> Define a release method for the ubd driver so that sysfs doesn't complain when one is removed.
> o-direct-field
> Last Changed - Mon Apr 3 08:56:21 EDT 2006
> This patch pulls the addition of the openflags.d field from externfs. This will be merged with the o_direct patch when it is sent to mainline.
> externfs-aio
> Last Changed - Wed Mar 22 15:20:24 EST 2006
> These are the AIO changes needed by the ubd driver and humfs.
> externfs
> Last Changed - Tue Apr 25 12:00:20 EDT 2006
> This is the externfs/new hostfs/humfs patch. hostfs now seems to be stable. The old hostfs will continue to exist until this one is as functional and stable as it.
> delete-hostfs
> Last Changed - Tue Apr 25 12:00:22 EDT 2006
> This deletes the old hostfs. This will be sent to mainline when the externfs-based hostfs seems stable.
> switch-pipe
> Last Changed - Mon Apr 3 09:01:40 EDT 2006
> This fixes the interface of make_pipe, which doesn't need to initialize filehandles. Instead, it is just a wrapper around pipe which just reclaims descriptors if the initial call to pipe failes with -EMFILE.
> fork-not-clone
> Last Changed - Mon Apr 3 09:01:44 EDT 2006
> Convert the boot-time host ptrace testing from clone to fork. They were essentially doing fork anyway. This cleans up the code a bit, and makes valgrind a bit happier about grinding it.
> fp-state
> Last Changed - Mon Apr 3 09:28:26 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> This patch is for testing only! It's a quick and dirty patch to verify, that wrong fp-context saving and restore really are the cause of errors in "memtest.c" It fixes the problem by: - making have_fpx_regs accessible for other modules instead of declaring it "static" in arch/um/os-Linux/sys-i386/registers.c - Adding 1 to HOST_FP_SIZE to have room for the "status" (and magic) field. Now skas.fp + skas.xfp combined have the size of struct _fpstatus - in arch/um/sys-i386/signal.c adding some code, that handles the _fpstatus in sigcontext differently, depending on have_fpx_regs. For (have_fpx_regs == 0), the _fpstatus simply is copied to/from user from/to skas.fp. When writing to user, the status field is created also. For (have_fpx_regs == 1), when writing to user, the full _fpstatus is created in skas.fp and skas.xfp, from the data found in skas.xfp. Then it is copied to user. When reading, the full _fpstatus is read to skas.fp and skas.xfp. Then, skas.xfp is reconstructed from this data.
> x11-fb
> Last Changed - Tue Apr 25 12:00:28 EDT 2006
> X11 framebuffer driver from Gerd Knorr. You have to enable CONFIG_FB (UML-specific options/Graphics support/ Support for frabe buffer devices), disable CONFIG_VGA_CONSOLE (UML-specific options/Graphics support/Console display driver support/ VGA text console), and enable Framebuffer Console support (in the same place), plus some fonts. You also seem to have to put 'x11=<width>x<height> on the command line.
> logging
> Last Changed - Mon Apr 3 09:05:12 EDT 2006
> This is a little logger which dumps stuff out to a host file. Used for tracking down otherwise intractable bugs.
> fix-get_user_pages
> Last Changed - Mon Apr 10 23:00:54 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> Fix of a wrong condition. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> add-stub-vmas.patch
> Last Changed - Mon Apr 10 23:02:17 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> This patch adds vm_area structs for stub-code and stub-data. So, stub-area is displayed in /proc/XXX/maps. Also, stub-pages are accessible for debuggers via ptrace now. Linux has a gate-vma concept, that unfortunately supports one gate-vma only. Thus, there need to be done some changes in mm/memory.c and fs/proc/task_mmu.c. This patch avoids the mainline changes by using some dirty tricks. So, the patch is for testing only, mainline should be changed to support more than one gate-vma.
> fix-jiffies.patch
> Last Changed - Mon Apr 3 15:00:12 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> To support different subarches, UML must not use the same address for jiffies and jiffies_64 in a hardcoded way. I added JIFFIES_OFFSET to handle different arches. For current arches, it is set to 0, for s390 it will be set to 4. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> insert-TIF_RESTART_SVC
> Last Changed - Tue Mar 21 11:57:39 EST 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> s390 syscalls might be done by a "svc X" instruction (2 bytes in size) or a "exec X,Y" instruction (4 bytes in size). There is no way to read the size of the instruction via ptrace, so UML/s390 can't do syscall-restarting by resetting instruction pointer to the value before the syscall. Also, in most cases syscall number is hardcoded in the "SVC X" instruction, so there is no way to handle ERESTART_RESTARTBLOCK correctly by *really* restarting the syscall. s390 host has implemented TIF_RESTART_SVC-flag to handle the latter case. In UML we have to use TIF_RESTART_SVC for both cases. This patch implements TIF_RESTART_SVC in UML. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> s390 syscalls might be done by a "svc X" instruction (2 bytes in size) or a "exec X,Y" instruction (4 bytes in size). There is no way to read the size of the instruction via ptrace, so UML/s390 can't do syscall-restarting by resetting instruction pointer to the value before the syscall. Also, in most cases syscall number is hardcoded in the "SVC X" instruction, so there is no way to handle ERESTART_RESTARTBLOCK correctly by *really* restarting the syscall. s390 host has implemented TIF_RESTART_SVC-flag to handle the latter case. In UML we have to use TIF_RESTART_SVC for both cases. This patch implements TIF_RESTART_SVC in UML. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> 390-syscall-restart
> Last Changed - Mon Apr 3 09:07:25 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> s390 normally doesn't support a method, that allows us to force the host to skip its syscall restart handling. I implemented a new method in the host, which also is posted to LKML to hopefully be inserted in s390 mainline. To check availability of this change, I added a new check, which is done in a slightly different way for the other arches, too. Success in check_ptrace() and success in the new check are absolutely necessary for UML to run in any mode. So I changed the sequence of checks to: 1) check_ptrace() being called at startup very early 2) check_ptrace() calls the new check, too 3) can_do_skas() is called after check_ptrace() check_ptrace() will never return, if it fails, but it now uses printf() and exit() instead of panic(). Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> fix-tt-USR1-handlers
> Last Changed - Mon Apr 3 09:07:28 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> UML: change tt-mode's USR1 handlers to be subarch independent Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> add-PTRACE_AREA
> Last Changed - Mon Apr 3 09:09:43 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> s390 doesn't have PTRACE_GETREGS and friends, but has PTRACE_[PEEK|POKE]USR_AREA to let user of ptrace() read or write struct user as he wants. So we need to support this operation conditionally. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> execve1-add-SUBARCH_EXECVE1
> Last Changed - Mon Apr 3 14:05:01 EDT 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> UML/s390 needs to reset FP control register in execve1, as Linux s390 does. I choose the way to use a macro, as this doesn't need any changes in the other subarches. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> boot_timer_handler-no-prototye
> Last Changed - Tue Mar 21 11:57:44 EST 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> On UML/s390, signal-handlers are defined to have 4 parameters, while the standard definition for signal-handlers only has one. So we must not have prototypes of the handlers using one param only in headers, that are included in the source, that defines the handlers. Just that conflict occurs with the incremental patches for 2.6.12-rc3. arch/um/os-Linux/signal.c defines boot_timer_handler to have 4 parameters (ARCH_SIGHDLR_PARAM), while arch/um/include/kern_util.h holds a prototype with one int as param only. With the latest patches, signal.c includes kern_util.h indirectly via os.h: build fails. So, I simply remove the prototype from kern_util.h and give each modules calling it a separate prototype. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> factor-handler-param
> Last Changed - Mon Apr 3 09:09:53 EDT 2006
> This puts the int sig back in the signal handler declarations. Before, with it in ARCH_SIGHDLR_PARAM, there was a use of sig, but no visible declaration.
> stub-arch-optimization
> Last Changed - Tue Mar 21 11:57:45 EST 2006
> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com> In s390, fpregs are not reset in signal handlers. Thus we may stop stub_segv_handler on s390 with a breakpoint instruction instead of calling getpid, kill and sigreturn. To make this run, we must not mask any signals in stub_segv_handler. So I added conditional execution of set_handler in userspace_tramp depending on ARCH_STUB_NO_SIGRETURN. If this macro isn't defined, the code remains unchanged, else no signals for sa_mask are defined and SA_NODEFER is added to flags. Using the change, we also no longer need to care about correct stack pointer for sigreturn, which would cause some nasty code on s390. Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
> test_stub_kill
> Last Changed - Tue Mar 21 11:57:46 EST 2006
> A small stub optimization. I forget what the reasoning was, needs more thought.
> s390
> Last Changed - Tue Mar 21 11:57:46 EST 2006
> This patch adds s390 (31-bit) to UML. SKAS0 and SKAS3 are tested a bit at least system boots and shuts down correctly, network (tun/tap) works and we even could start YaST on it. Note:s We use a host running SuSE SLES8 with a "private" kernel named 2.4.21-fsc.11, that contains special adaptions and drivers for Fujitsu-Siemens mainframes. This means, our current SKAS3-patch doesn't fit to vanilla kernels. We will create a reworked patch for vanilla later (2.4 and 2.6). Our 2.4 kernel also contains two fixes and one enhancement, that all are essential to make UML run, even in SKAS0. The enhancement is to support PT_TRACESYSGOOD, that generally is available in 2.6 kernels but not in 2.4 for s390. So I would suggest to use 2.6 host for the moment. The fixes meanwhile are included into mainline. I don't know precisely the first version containing them, in 2.6.13-rc5 they are present. As those two patches are very small, they are inserted here as as comment (AFAICS, its easy to do the changes by hand on older kernel versions): First patch to fix signal stack handling: --- a/arch/s390/kernel/signal.c 2005-03-22 11:07:39.000000000 +0100 +++ b/arch/s390/kernel/signal.c 2005-03-22 11:08:44.000000000 +0100 @@ -285,7 +285,7 @@ /* This is the X/Open sanctioned signal stack switching. */ if (ka->sa.sa_flags & SA_ONSTACK) { - if (! on_sig_stack(sp)) + if (! sas_ss_flags(sp)) sp = current->sas_ss_sp + current->sas_ss_size; } Second patch to allow skipping of syscall restart: --- a/arch/s390/kernel/ptrace.c 2005-05-07 07:20:31.000000000 +0200 +++ b/arch/s390/kernel/ptrace.c 2005-08-02 06:45:48.000000000 +0200 @@ -723,6 +761,13 @@ ? 0x80 : 0)); /* + * If the debugger has set an invalid system call number, + * we prepare to skip the system call restart handling. + */ + if (!entryexit && regs->gprs[2] >= NR_syscalls) + regs->trap = -1; + + /* * this isn't the same as continuing with a signal, but it will do * for normal use. strace only continues with a signal if the * stopping signal is not SIGTRAP. -brl
> ubd-aio
> Last Changed - Mon Apr 3 13:40:46 EDT 2006
> This adds AIO support to the ubd driver.
> ubd-drop-lock
> Last Changed - Mon Apr 3 13:43:37 EDT 2006
> This patch changes the ubd I/O submission process to avoid some sleeping. When the host returns -EAGAIN from io_submit, do_ubd_request returns to its caller, saving the current state of the request submission in the struct ubd. This state consists of the request structure and the range of sg entries which have not yet been submitted. If the request queue is drained, then this state is reset to indicate that, the next time it is called, a new request needs to be pulled from the request queue. When do_ubd_request returns because the host can handle no more requests, it is necessary to rerun the queue after some completions have been handled. This is done by adding the device to the restart list. ubd_intr walks this list before returning, calling do_ubd_request for each device. In addition, the queues and queue locks are now per-device, rather than having a single queue and lock for all devices. Note that kmalloc is still called, and can sleep. This is fixed in a future patch. This patch changes the ubd I/O submission process to avoid some sleeping. When the host returns -EAGAIN from io_submit, do_ubd_request returns to its caller, saving the current state of the request submission in the struct ubd. This state consists of the request structure and the range of sg entries which have not yet been submitted. If the request queue is drained, then this state is reset to indicate that, the next time it is called, a new request needs to be pulled from the request queue. When do_ubd_request returns because the host can handle no more requests, it is necessary to rerun the queue after some completions have been handled. This is done by adding the device to the restart list. ubd_intr walks this list before returning, calling do_ubd_request for each device. In addition, the queues and queue locks are now per-device, rather than having a single queue and lock for all devices. Note that kmalloc is still called, and can sleep. This is fixed in a future patch.
> ubd-atomic
> Last Changed - Mon Apr 3 13:43:45 EDT 2006
> To ensure that I/O can always make progress, even when there is no memory, we provide static buffers which are to be used when dynamic ones can't be allocated. These buffers are protected by flags which are set when they are currently in use. The use of these flags is protected by the queue lock, which is held for the duration of the do_ubd_request call. There is an allocation failure emulation mechanism here - setting fail_start and fail_end will cause allocations in that range (fail_start <= allocations < fail_end) to fail, invoking the emergency mechanism. When this is happening, I/O requests proceed one at a time, essentially synchronously, until allocations start succeeding again. This currently doesn't handle the bitmap array, since that can be of any length, so we can't have a static version of it at this point.
> bitmap-atomic
> Last Changed - Mon Apr 3 14:02:09 EDT 2006
> This patch completes the robustness and deadlock avoidance work by handling the writing of the bitmap. The existing method of dealing with low-memory situations by having an emergency structure for use when memory can't be allocated won't work here because of the variable size of the bitmap buffer, and the unknown (to me) limit of a contiguous I/O request. The allocation is avoided by writing directly from the bitmap rather than allocating a buffer and copying the relevant chunk of the bitmap into it. This has a number of consequences. First, since the bitmap is written directly from the device's bitmap, bits should not be set in it until the I/O is just about to start. This is because reads would see that and possibly race with the outgoing writes, returning data from a section of the COW file which has never been written. To prevent this, reads that overlap a pending bitmap write are stalled until the write is finished. Modifying the bitmap bits as late as possible shrinks the window in which this could happen. Second, a section of bitmap that's being written out should not be modified again until the write has finished. Otherwise, a bit might be set and picked up by a pending I/O, resulting in it being on disk too soon. So, there are a couple new lists. Bitmap writes which have been issued, but not finished are on the pending_bitmaps list. Any subsequent bitmap writes which overlap a pending write have to wait. These are put on the waiting_bitmaps list. Whenever a pending bitmap write finishes, any overlapping waiting writes are tried. They may continue waiting because they overlap an earlier waiter, but at least one will proceed. Third, reads which overlap a pending or waiting bitmap write will wait until those writes have finished. This is done by do_io returning -EAGAIN, causing the queue to wait until some requests have finished. This patch completes the robustness and deadlock avoidance work by handling the writing of the bitmap. The existing method of dealing with low-memory situations by having an emergency structure for use when memory can't be allocated won't work here because of the variable size of the bitmap buffer, and the unknown (to me) limit of a contiguous I/O request. The allocation is avoided by writing directly from the bitmap rather than allocating a buffer and copying the relevant chunk of the bitmap into it. This has a number of consequences. First, since the bitmap is written directly from the device's bitmap, bits should not be set in it until the I/O is just about to start. This is because reads would see that and possibly race with the outgoing writes, returning data from a section of the COW file which has never been written. To prevent this, reads that overlap a pending bitmap write are stalled until the write is finished. Modifying the bitmap bits as late as possible shrinks the window in which this could happen. Second, a section of bitmap that's being written out should not be modified again until the write has finished. Otherwise, a bit might be set and picked up by a pending I/O, resulting in it being on disk too soon. So, there are a couple new lists. Bitmap writes which have been issued, but not finished are on the pending_bitmaps list. Any subsequent bitmap writes which overlap a pending write have to wait. These are put on the waiting_bitmaps list. Whenever a pending bitmap write finishes, any overlapping waiting writes are tried. They may continue waiting because they overlap an earlier waiter, but at least one will proceed. Third, reads which overlap a pending or waiting bitmap write will wait until those writes have finished. This is done by do_io returning -EAGAIN, causing the queue to wait until some requests have finished.
> non-aio-deadlock
> Last Changed - Tue Mar 21 11:57:50 EST 2006
> The pipe to the AIO thread needs to be non-blocking so that we know when to return -EAGAIN and process some completions before trying some more requests.
> ubd-no-count
> Last Changed - Mon Apr 3 13:50:36 EDT 2006
> This patch eliminates the atomic count associated with a bitmap_io struct. The original thinking was that there would be a number of aio structures associated with the bitmap_io, since different chunks of the sg element could go to different layers. The count was needed to know when the full sg segment reached disk and it was safe to write the bitmap. However, the flaw in that thinking is that a bitmap_io struct is only needed for writes, and writes always go to the COW layer. Hence, there will only be one bitmap_io per aio, and the counting is unnecessary. This patch makes it possible to merge the aio and bitmap_io structs, which would be a good cleanup.
> init_aio_err
> Last Changed - Tue Mar 21 11:57:51 EST 2006
> Tidy the error handling in the AIO initialization.
> aio-batching
> Last Changed - Mon Apr 3 14:06:59 EDT 2006
> I noticed that the common case in io_submit is an immediate context switch to the AIO thread when it returns from io_getevents, followed by a switch back. This patch changes that by having the AIO thread wait on a pipe before calling io_getevents. When the kernel finishes a batch of I/O, it writes the number of requests down the pipe, and the AIO thread waits for that number, and goes back to sleeping on the pipe. This probably shouldn't reach mainline, as O_DIRECT I/O should have the property of causing switching on every I/O request. Also, the wakeup mechanism should be only used when the other side might be sleeping. I noticed that the common case in io_submit is an immediate context switch to the AIO thread when it returns from io_getevents, followed by a switch back. This patch changes that by having the AIO thread wait on a pipe before calling io_getevents. When the kernel finishes a batch of I/O, it writes the number of requests down the pipe, and the AIO thread waits for that number, and goes back to sleeping on the pipe. This probably shouldn't reach mainline, as O_DIRECT I/O should have the property of causing switching on every I/O request. Also, the wakeup mechanism should be only used when the other side might be sleeping.
> o_direct
> Last Changed - Mon Apr 3 13:53:03 EDT 2006
> This enables O_DIRECT on ubd devices. This needs work, as it will die when creating a COW file. It also needs to do buffered I/O on backing files.
> init-io-req
> Last Changed - Mon Apr 3 13:53:05 EDT 2006
> This uses the C99 syntax to initialize an io_thread_req. Given how this is compiled, it may not be a good idea, as it will consume more stack than it should.
> no-o-direct
> Last Changed - Mon Apr 3 09:18:14 EDT 2006
> This is the reversion of the o_direct patch so I can make COW files.
> no-fakehd
> Last Changed - Fri Mar 24 14:48:53 EST 2006
> The fakehd switch lost its implementation at some point. Since no one is screaming for it, we might as well remove it.
> cow-odirect
> Last Changed - Mon Apr 3 14:02:43 EDT 2006
> Start fixing the problems with aligned access to COW files when O_DIRECT is enabled.
> fuse
> Last Changed - Thu Apr 13 13:18:24 EDT 2006
> This is the start of the FUSE server support, which will export the UML filesystem to the host as a FUSE filesystem.
> no-cow-odirect
> Last Changed - Mon Apr 3 14:03:02 EDT 2006
> Back out the odirect stuff temporarily.
> fix-humfs
> Last Changed - Mon Apr 3 08:47:32 EDT 2006
> Fixes to humfs, which haven't been merged back into externfs yet.
> no-sigjmpbuf
> Last Changed - Mon Apr 3 15:46:53 EDT 2006
> Clean up the jmpbuf code. Since softints, we no longer use sig_setjmp, so the UML_SIGSETJMP wrapper now has a misleading name. Also, I forgot to change the buffers from sigjmp_buf to jmp_buf.
> fix-errno
> Last Changed - Wed Apr 26 17:50:44 EDT 2006
> Blairsorblade noticed some confusion between a system call's return value and errno. This patch fixes a number of related bugs - using errno instead of a return value using a return value instead of errno forgetting to negate a error return to get a positive error code
> 2g
> Last Changed - Wed Apr 26 17:55:40 EDT 2006
> From Joris van Rantwijk <jvrantwijk@xs4all.nl>: A quick hack to allow skas0 mode to run on 2G/2G hosts.
> jesper-cleanups
> Last Changed - Wed Apr 26 15:40:48 EDT 2006
Remove redundant NULL checks before [kv]free + small CodingStyle cleanup for arch/ Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>

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