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F_READAHEAD: Fix r349248's overflow protection, broken by r349391

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I accidentally broke the main point of r349248 when making stylistic changes
in r349391.  Restore the original behavior, and also fix an additional
overflow that was possible when uio->uio_resid was nearly SSIZE_MAX.

Reported by:	cem
Reviewed by:	bde
MFC after:	2 weeks
MFC-With:	349248
Sponsored by:	The FreeBSD Foundation
This commit is contained in:
Alan Somers 2019-07-17 17:01:07 +00:00
parent 0660822abb
commit 0122532ee0
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=350088
1 changed files with 7 additions and 2 deletions
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9
sys/kern/vfs_vnops.c
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@ -499,8 +499,13 @@ sequential_heuristic(struct uio *uio, struct file *fp)
* closely related to the best I/O size for real disks than
* to any block size used by software.
*/
fp->f_seqcount += lmin(IO_SEQMAX,
howmany(uio->uio_resid, 16384));
if (uio->uio_resid >= IO_SEQMAX * 16384)
fp->f_seqcount = IO_SEQMAX;
else {
fp->f_seqcount += howmany(uio->uio_resid, 16384);
if (fp->f_seqcount > IO_SEQMAX)
fp->f_seqcount = IO_SEQMAX;
}
return (fp->f_seqcount << IO_SEQSHIFT);
}