1. 12 Jan, 2006 1 commit
  2. 10 Jan, 2006 1 commit
    • Alan Cox's avatar
      [PATCH] TTY layer buffering revamp · 33f0f88f
      Alan Cox authored
      The API and code have been through various bits of initial review by
      serial driver people but they definitely need to live somewhere for a
      while so the unconverted drivers can get knocked into shape, existing
      drivers that have been updated can be better tuned and bugs whacked out.
      
      This replaces the tty flip buffers with kmalloc objects in rings. In the
      normal situation for an IRQ driven serial port at typical speeds the
      behaviour is pretty much the same, two buffers end up allocated and the
      kernel cycles between them as before.
      
      When there are delays or at high speed we now behave far better as the
      buffer pool can grow a bit rather than lose characters. This also means
      that we can operate at higher speeds reliably.
      
      For drivers that receive characters in blocks (DMA based, USB and
      especially virtualisation) the layer allows a lot of driver specific
      code that works around the tty layer with private secondary queues to be
      removed. The IBM folks need this sort of layer, the smart serial port
      people do, the virtualisers do (because a virtualised tty typically
      operates at infinite speed rather than emulating 9600 baud).
      
      Finally many drivers had invalid and unsafe attempts to avoid buffer
      overflows by directly invoking tty methods extracted out of the innards
      of work queue structs. These are no longer needed and all go away. That
      fixes various random hangs with serial ports on overflow.
      
      The other change in here is to optimise the receive_room path that is
      used by some callers. It turns out that only one ldisc uses receive room
      except asa constant and it updates it far far less than the value is
      read. We thus make it a variable not a function call.
      
      I expect the code to contain bugs due to the size alone but I'll be
      watching and squashing them and feeding out new patches as it goes.
      
      Because the buffers now dynamically expand you should only run out of
      buffering when the kernel runs out of memory for real.  That means a lot of
      the horrible hacks high performance drivers used to do just aren't needed any
      more.
      
      Description:
      
      tty_insert_flip_char is an old API and continues to work as before, as does
      tty_flip_buffer_push() [this is why many drivers dont need modification].  It
      does now also return the number of chars inserted
      
      There are also
      
      tty_buffer_request_room(tty, len)
      
      which asks for a buffer block of the length requested and returns the space
      found.  This improves efficiency with hardware that knows how much to
      transfer.
      
      and tty_insert_flip_string_flags(tty, str, flags, len)
      
      to insert a string of characters and flags
      
      For a smart interface the usual code is
      
          len = tty_request_buffer_room(tty, amount_hardware_says);
          tty_insert_flip_string(tty, buffer_from_card, len);
      
      More description!
      
      At the moment tty buffers are attached directly to the tty.  This is causing a
      lot of the problems related to tty layer locking, also problems at high speed
      and also with bursty data (such as occurs in virtualised environments)
      
      I'm working on ripping out the flip buffers and replacing them with a pool of
      dynamically allocated buffers.  This allows both for old style "byte I/O"
      devices and also helps virtualisation and smart devices where large blocks of
      data suddenely materialise and need storing.
      
      So far so good.  Lots of drivers reference tty->flip.*.  Several of them also
      call directly and unsafely into function pointers it provides.  This will all
      break.  Most drivers can use tty_insert_flip_char which can be kept as an API
      but others need more.
      
      At the moment I've added the following interfaces, if people think more will
      be needed now is a good time to say
      
       int tty_buffer_request_room(tty, size)
      
      Try and ensure at least size bytes are available, returns actual room (may be
      zero).  At the moment it just uses the flipbuf space but that will change.
      Repeated calls without characters being added are not cumulative.  (ie if you
      call it with 1, 1, 1, and then 4 you'll have four characters of space.  The
      other functions will also try and grow buffers in future but this will be a
      more efficient way when you know block sizes.
      
       int tty_insert_flip_char(tty, ch, flag)
      
      As before insert a character if there is room.  Now returns 1 for success, 0
      for failure.
      
       int tty_insert_flip_string(tty, str, len)
      
      Insert a block of non error characters.  Returns the number inserted.
      
       int tty_prepare_flip_string(tty, strptr, len)
      
      Adjust the buffer to allow len characters to be added.  Returns a buffer
      pointer in strptr and the length available.  This allows for hardware that
      needs to use functions like insl or mencpy_fromio.
      Signed-off-by: default avatarAlan Cox <alan@redhat.com>
      Cc: Paul Fulghum <paulkf@microgate.com>
      Signed-off-by: default avatarHirokazu Takata <takata@linux-m32r.org>
      Signed-off-by: default avatarSerge Hallyn <serue@us.ibm.com>
      Signed-off-by: default avatarJeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarJohn Hawkes <hawkes@sgi.com>
      Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
      Signed-off-by: default avatarAdrian Bunk <bunk@stusta.de>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      33f0f88f
  3. 07 Nov, 2005 1 commit
  4. 31 Oct, 2005 1 commit
  5. 28 Oct, 2005 1 commit
  6. 09 Sep, 2005 3 commits
    • Dipankar Sarma's avatar
      [PATCH] files: lock-free fd look-up · b835996f
      Dipankar Sarma authored
      With the use of RCU in files structure, the look-up of files using fds can now
      be lock-free.  The lookup is protected by rcu_read_lock()/rcu_read_unlock().
      This patch changes the readers to use lock-free lookup.
      Signed-off-by: default avatarManeesh Soni <maneesh@in.ibm.com>
      Signed-off-by: default avatarRavikiran Thirumalai <kiran_th@gmail.com>
      Signed-off-by: default avatarDipankar Sarma <dipankar@in.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      b835996f
    • Dipankar Sarma's avatar
      [PATCH] files: break up files struct · badf1662
      Dipankar Sarma authored
      In order for the RCU to work, the file table array, sets and their sizes must
      be updated atomically.  Instead of ensuring this through too many memory
      barriers, we put the arrays and their sizes in a separate structure.  This
      patch takes the first step of putting the file table elements in a separate
      structure fdtable that is embedded withing files_struct.  It also changes all
      the users to refer to the file table using files_fdtable() macro.  Subsequent
      applciation of RCU becomes easier after this.
      Signed-off-by: default avatarDipankar Sarma <dipankar@in.ibm.com>
      Signed-Off-By: default avatarDavid Howells <dhowells@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      badf1662
    • Jason Baron's avatar
      [PATCH] pty_chars_in_buffer oops fix · ff55fe20
      Jason Baron authored
      The idea of this patch is to lock both sides of a ptmx/pty pair during line
      discipline changing.  This is needed to ensure that say a poll on one side of
      the pty doesn't occur while the line discipline is actively being changed.
      This resulted in an oops reported on lkml, see:
      
      	http://marc.theaimsgroup.com/?l=linux-kernel&m=111342171410005&w=2
      
      A 'hacky' approach was previously implmemented which served to eliminate the
      poll vs.  line discipline changing race.  However, this patch takes a more
      general approach to the issue.  The patch only adds locking on a less often
      used path, the line-discipline changing path, as opposed to locking the
      ptmx/pty pair on read/write/poll paths.
      
      The patch below, takes both ldisc locks in either order b/c the locks are both
      taken under the same spinlock().  I thought about locking the ptmx/pty
      separately, such as master always first but that introduces a 3 way deadlock.
      For example, process 1 does a blocking read on the slave side.  Then, process
      2 does an ldisc change on the slave side, which acquires the master ldisc lock
      but not the slave's.  Finally, process 3 does a write which blocks on the
      process 2's ldisc reference.
      
      This patch does introduce some changes in semantics.  For example, a line
      discipline change on side 'a' of a ptmx/pty pair, will now wait for a
      read/write to complete on the other side, or side 'b'.  The current behavior
      is to simply wait for any read/writes on only side 'a', not both sides 'a' and
      'b'.  I think this behavior makes sense, but I wanted to point it out.
      
      I've tested the patch with a bunch of read/write/poll while changing the line
      discipline out from underneath.
      
      This patch obviates the need for the above "hide the problem" patch.
      Signed-off-by: default avatarJason Baron <jbaron@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      ff55fe20
  7. 07 Sep, 2005 1 commit
  8. 25 Jun, 2005 1 commit
  9. 23 Jun, 2005 1 commit
  10. 20 Jun, 2005 1 commit
  11. 05 May, 2005 1 commit
  12. 16 Apr, 2005 1 commit
    • Linus Torvalds's avatar
      Linux-2.6.12-rc2 · 1da177e4
      Linus Torvalds authored
      Initial git repository build. I'm not bothering with the full history,
      even though we have it. We can create a separate "historical" git
      archive of that later if we want to, and in the meantime it's about
      3.2GB when imported into git - space that would just make the early
      git days unnecessarily complicated, when we don't have a lot of good
      infrastructure for it.
      
      Let it rip!
      1da177e4