Add two new fcntls to enable/disable read-ahead:
- F_READAHEAD: specify the amount for sequential access. The amount is specified in bytes and is rounded up to nearest block size. - F_RDAHEAD: Darwin compatible version that use 128KB as the sequential access size. A third argument of zero disables the read-ahead behavior. Please note that the read-ahead amount is also constrainted by sysctl variable, vfs.read_max, which may need to be raised in order to better utilize this feature. Thanks Igor Sysoev for proposing the feature and submitting the original version, and kib@ for his valuable comments. Submitted by: Igor Sysoev <is rambler-co ru> Reviewed by: kib@ MFC after: 1 month
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=197579
@ -28,7 +28,7 @@
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.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
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.\" $FreeBSD$
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.\"
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.Dd March 8, 2008
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.Dd September 28, 2009
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.Dt FCNTL 2
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.Os
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.Sh NAME
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@ -241,6 +241,22 @@ will be interrupted if the signal handler has not specified the
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.Dv SA_RESTART
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(see
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.Xr sigaction 2 ) .
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.It Dv F_READAHEAD
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Set or clear the read ahead amount for sequential access to the third
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argument,
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.Fa arg ,
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which is rounded up to the nearest block size.
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A zero value in
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.Fa arg
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turns off read ahead.
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.It Dv F_RDAHEAD
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Equivalent to Darwin counterpart which sets read ahead amount of 128KB
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when the third argument,
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.Fa arg
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is non-zero.
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A zero value in
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.Fa arg
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turns off read ahead.
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.El
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.Pp
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When a shared lock has been set on a segment of a file,
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@ -421,6 +421,8 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
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struct vnode *vp;
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int error, flg, tmp;
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int vfslocked;
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u_int old, new;
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uint64_t bsize;
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vfslocked = 0;
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error = 0;
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@ -686,6 +688,48 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
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vfslocked = 0;
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fdrop(fp, td);
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break;
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case F_RDAHEAD:
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arg = arg ? 128 * 1024: 0;
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/* FALLTHROUGH */
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case F_READAHEAD:
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FILEDESC_SLOCK(fdp);
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if ((fp = fdtofp(fd, fdp)) == NULL) {
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FILEDESC_SUNLOCK(fdp);
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error = EBADF;
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break;
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}
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if (fp->f_type != DTYPE_VNODE) {
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FILEDESC_SUNLOCK(fdp);
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error = EBADF;
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break;
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}
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fhold(fp);
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FILEDESC_SUNLOCK(fdp);
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if (arg != 0) {
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vp = fp->f_vnode;
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vfslocked = VFS_LOCK_GIANT(vp->v_mount);
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error = vn_lock(vp, LK_SHARED);
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if (error != 0)
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goto readahead_vnlock_fail;
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bsize = fp->f_vnode->v_mount->mnt_stat.f_iosize;
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VOP_UNLOCK(vp, 0);
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fp->f_seqcount = (arg + bsize - 1) / bsize;
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do {
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new = old = fp->f_flag;
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new |= FRDAHEAD;
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} while (atomic_cmpset_rel_int(&fp->f_flag, old, new) == 0);
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readahead_vnlock_fail:
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VFS_UNLOCK_GIANT(vfslocked);
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} else {
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do {
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new = old = fp->f_flag;
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new &= ~FRDAHEAD;
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} while (atomic_cmpset_rel_int(&fp->f_flag, old, new) == 0);
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}
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fdrop(fp, td);
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break;
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default:
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error = EINVAL;
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break;
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@ -312,6 +312,9 @@ static int
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sequential_heuristic(struct uio *uio, struct file *fp)
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{
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if (atomic_load_acq_int(&(fp->f_flag)) & FRDAHEAD)
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return (fp->f_seqcount << IO_SEQSHIFT);
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/*
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* Offset 0 is handled specially. open() sets f_seqcount to 1 so
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* that the first I/O is normally considered to be slightly
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@ -140,7 +140,7 @@ typedef __pid_t pid_t;
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/* bits to save after open */
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#define FMASK (FREAD|FWRITE|FAPPEND|FASYNC|FFSYNC|FNONBLOCK|O_DIRECT|FEXEC)
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/* bits settable by fcntl(F_SETFL, ...) */
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|O_DIRECT)
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FRDAHEAD|O_DIRECT)
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#if defined(COMPAT_FREEBSD7) || defined(COMPAT_FREEBSD6) || \
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defined(COMPAT_FREEBSD5) || defined(COMPAT_FREEBSD4)
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@ -151,7 +151,8 @@ typedef __pid_t pid_t;
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*/
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#define FPOSIXSHM O_NOFOLLOW
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#undef FCNTLFLAGS
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FPOSIXSHM|O_DIRECT)
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#define FCNTLFLAGS (FAPPEND|FASYNC|FFSYNC|FNONBLOCK|FPOSIXSHM|FRDAHEAD| \
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O_DIRECT)
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#endif
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#endif
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@ -176,6 +177,8 @@ typedef __pid_t pid_t;
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* different meaning for fcntl(2).
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*/
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#if __BSD_VISIBLE
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/* Read ahead */
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#define FRDAHEAD O_CREAT
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#endif
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/* Defined by POSIX Extended API Set Part 2 */
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@ -218,6 +221,8 @@ typedef __pid_t pid_t;
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#define F_SETLK 12 /* set record locking information */
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#define F_SETLKW 13 /* F_SETLK; wait if blocked */
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#define F_SETLK_REMOTE 14 /* debugging support for remote locks */
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#define F_READAHEAD 15 /* read ahead */
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#define F_RDAHEAD 16 /* Darwin compatible read ahead */
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/* file descriptor flags (F_GETFD, F_SETFD) */
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#define FD_CLOEXEC 1 /* close-on-exec flag */
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