15 Oct, 2010

1 commit

• 6038f373a   llseek: automatically add .llseek fop ... Browse Code »

  All file_operations should get a .llseek operation so we can make
  nonseekable_open the default for future file operations without a
  .llseek pointer.

  The three cases that we can automatically detect are no_llseek, seq_lseek
  and default_llseek. For cases where we can we can automatically prove that
  the file offset is always ignored, we use noop_llseek, which maintains
  the current behavior of not returning an error from a seek.

  New drivers should normally not use noop_llseek but instead use no_llseek
  and call nonseekable_open at open time. Existing drivers can be converted
  to do the same when the maintainer knows for certain that no user code
  relies on calling seek on the device file.

  The generated code is often incorrectly indented and right now contains
  comments that clarify for each added line why a specific variant was
  chosen. In the version that gets submitted upstream, the comments will
  be gone and I will manually fix the indentation, because there does not
  seem to be a way to do that using coccinelle.

  Some amount of new code is currently sitting in linux-next that should get
  the same modifications, which I will do at the end of the merge window.

  Many thanks to Julia Lawall for helping me learn to write a semantic
  patch that does all this.

  ===== begin semantic patch =====
  // This adds an llseek= method to all file operations,
  // as a preparation for making no_llseek the default.
  //
  // The rules are
  // - use no_llseek explicitly if we do nonseekable_open
  // - use seq_lseek for sequential files
  // - use default_llseek if we know we access f_pos
  // - use noop_llseek if we know we don't access f_pos,
  // but we still want to allow users to call lseek
  //
  @ open1 exists @
  identifier nested_open;
  @@
  nested_open(...)
  {

  }

  @ open exists@
  identifier open_f;
  identifier i, f;
  identifier open1.nested_open;
  @@
  int open_f(struct inode *i, struct file *f)
  {

  }

  @ read disable optional_qualifier exists @
  identifier read_f;
  identifier f, p, s, off;
  type ssize_t, size_t, loff_t;
  expression E;
  identifier func;
  @@
  ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
  {

  }

  @ read_no_fpos disable optional_qualifier exists @
  identifier read_f;
  identifier f, p, s, off;
  type ssize_t, size_t, loff_t;
  @@
  ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
  {
  ... when != off
  }

  @ write @
  identifier write_f;
  identifier f, p, s, off;
  type ssize_t, size_t, loff_t;
  expression E;
  identifier func;
  @@
  ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
  {

  }

  @ write_no_fpos @
  identifier write_f;
  identifier f, p, s, off;
  type ssize_t, size_t, loff_t;
  @@
  ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
  {
  ... when != off
  }

  @ fops0 @
  identifier fops;
  @@
  struct file_operations fops = {
  ...
  };

  @ has_llseek depends on fops0 @
  identifier fops0.fops;
  identifier llseek_f;
  @@
  struct file_operations fops = {
  ...
  .llseek = llseek_f,
  ...
  };

  @ has_read depends on fops0 @
  identifier fops0.fops;
  identifier read_f;
  @@
  struct file_operations fops = {
  ...
  .read = read_f,
  ...
  };

  @ has_write depends on fops0 @
  identifier fops0.fops;
  identifier write_f;
  @@
  struct file_operations fops = {
  ...
  .write = write_f,
  ...
  };

  @ has_open depends on fops0 @
  identifier fops0.fops;
  identifier open_f;
  @@
  struct file_operations fops = {
  ...
  .open = open_f,
  ...
  };

  // use no_llseek if we call nonseekable_open
  ////////////////////////////////////////////
  @ nonseekable1 depends on !has_llseek && has_open @
  identifier fops0.fops;
  identifier nso ~= "nonseekable_open";
  @@
  struct file_operations fops = {
  ... .open = nso, ...
  +.llseek = no_llseek, /* nonseekable */
  };

  @ nonseekable2 depends on !has_llseek @
  identifier fops0.fops;
  identifier open.open_f;
  @@
  struct file_operations fops = {
  ... .open = open_f, ...
  +.llseek = no_llseek, /* open uses nonseekable */
  };

  // use seq_lseek for sequential files
  /////////////////////////////////////
  @ seq depends on !has_llseek @
  identifier fops0.fops;
  identifier sr ~= "seq_read";
  @@
  struct file_operations fops = {
  ... .read = sr, ...
  +.llseek = seq_lseek, /* we have seq_read */
  };

  // use default_llseek if there is a readdir
  ///////////////////////////////////////////
  @ fops1 depends on !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier readdir_e;
  @@
  // any other fop is used that changes pos
  struct file_operations fops = {
  ... .readdir = readdir_e, ...
  +.llseek = default_llseek, /* readdir is present */
  };

  // use default_llseek if at least one of read/write touches f_pos
  /////////////////////////////////////////////////////////////////
  @ fops2 depends on !fops1 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier read.read_f;
  @@
  // read fops use offset
  struct file_operations fops = {
  ... .read = read_f, ...
  +.llseek = default_llseek, /* read accesses f_pos */
  };

  @ fops3 depends on !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier write.write_f;
  @@
  // write fops use offset
  struct file_operations fops = {
  ... .write = write_f, ...
  + .llseek = default_llseek, /* write accesses f_pos */
  };

  // Use noop_llseek if neither read nor write accesses f_pos
  ///////////////////////////////////////////////////////////

  @ fops4 depends on !fops1 && !fops2 && !fops3 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier read_no_fpos.read_f;
  identifier write_no_fpos.write_f;
  @@
  // write fops use offset
  struct file_operations fops = {
  ...
  .write = write_f,
  .read = read_f,
  ...
  +.llseek = noop_llseek, /* read and write both use no f_pos */
  };

  @ depends on has_write && !has_read && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier write_no_fpos.write_f;
  @@
  struct file_operations fops = {
  ... .write = write_f, ...
  +.llseek = noop_llseek, /* write uses no f_pos */
  };

  @ depends on has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  identifier read_no_fpos.read_f;
  @@
  struct file_operations fops = {
  ... .read = read_f, ...
  +.llseek = noop_llseek, /* read uses no f_pos */
  };

  @ depends on !has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
  identifier fops0.fops;
  @@
  struct file_operations fops = {
  ...
  +.llseek = noop_llseek, /* no read or write fn */
  };
  ===== End semantic patch =====

  Signed-off-by: Arnd Bergmann
  Cc: Julia Lawall
  Cc: Christoph Hellwig

  Arnd Bergmann

  2010-10-15 21:53:27 +0800  

01 Oct, 2006

1 commit

• 9361401eb   [PATCH] BLOCK: Make it possible to disable the block layer [try #6] ... Browse Code »

  Make it possible to disable the block layer. Not all embedded devices require
  it, some can make do with just JFFS2, NFS, ramfs, etc - none of which require
  the block layer to be present.

  This patch does the following:

  (*) Introduces CONFIG_BLOCK to disable the block layer, buffering and blockdev
  support.

  (*) Adds dependencies on CONFIG_BLOCK to any configuration item that controls
  an item that uses the block layer. This includes:

  (*) Block I/O tracing.

  (*) Disk partition code.

  (*) All filesystems that are block based, eg: Ext3, ReiserFS, ISOFS.

  (*) The SCSI layer. As far as I can tell, even SCSI chardevs use the
  block layer to do scheduling. Some drivers that use SCSI facilities -
  such as USB storage - end up disabled indirectly from this.

  (*) Various block-based device drivers, such as IDE and the old CDROM
  drivers.

  (*) MTD blockdev handling and FTL.

  (*) JFFS - which uses set_bdev_super(), something it could avoid doing by
  taking a leaf out of JFFS2's book.

  (*) Makes most of the contents of linux/blkdev.h, linux/buffer_head.h and
  linux/elevator.h contingent on CONFIG_BLOCK being set. sector_div() is,
  however, still used in places, and so is still available.

  (*) Also made contingent are the contents of linux/mpage.h, linux/genhd.h and
  parts of linux/fs.h.

  (*) Makes a number of files in fs/ contingent on CONFIG_BLOCK.

  (*) Makes mm/bounce.c (bounce buffering) contingent on CONFIG_BLOCK.

  (*) set_page_dirty() doesn't call __set_page_dirty_buffers() if CONFIG_BLOCK
  is not enabled.

  (*) fs/no-block.c is created to hold out-of-line stubs and things that are
  required when CONFIG_BLOCK is not set:

  (*) Default blockdev file operations (to give error ENODEV on opening).

  (*) Makes some /proc changes:

  (*) /proc/devices does not list any blockdevs.

  (*) /proc/diskstats and /proc/partitions are contingent on CONFIG_BLOCK.

  (*) Makes some compat ioctl handling contingent on CONFIG_BLOCK.

  (*) If CONFIG_BLOCK is not defined, makes sys_quotactl() return -ENODEV if
  given command other than Q_SYNC or if a special device is specified.

  (*) In init/do_mounts.c, no reference is made to the blockdev routines if
  CONFIG_BLOCK is not defined. This does not prohibit NFS roots or JFFS2.

  (*) The bdflush, ioprio_set and ioprio_get syscalls can now be absent (return
  error ENOSYS by way of cond_syscall if so).

  (*) The seclvl_bd_claim() and seclvl_bd_release() security calls do nothing if
  CONFIG_BLOCK is not set, since they can't then happen.

  Signed-Off-By: David Howells
  Signed-off-by: Jens Axboe

  David Howells

  2006-10-01 02:52:31 +0800