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tarfs: Implement VOP_BMAP

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This lets tarfs provide readahead/behind hints to the VFS, which helps
memory-mapped I/O performance, important when running faulting in
executables out of a tarfs mount as one might if tarfs is used to back
the root filesystem, for example.  The improvement is particularly
noticeable when the backing tarball is zstd-compressed.

The implementation simply returns the extent of the virtual block
containing the target offset, clamped by the maximum I/O size.  This is
perhaps simplistic; it effectively just chooses values that would
correspond to a single VOP_READ call in tarfs_read_file().

Reviewed by:	des, kib
MFC after:	1 month
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D44626
This commit is contained in:
Mark Johnston 2024-04-05 11:14:36 -04:00
parent 663a704a58
commit a0895e394d
1 changed files with 55 additions and 0 deletions
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55
sys/fs/tarfs/tarfs_vnops.c
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@ -125,6 +125,60 @@ tarfs_access(struct vop_access_args *ap)
return (error);
}
static int
tarfs_bmap(struct vop_bmap_args *ap)
{
struct tarfs_node *tnp;
struct vnode *vp;
off_t off;
uint64_t iosize;
int ra, rb, rmax;
vp = ap->a_vp;
iosize = vp->v_mount->mnt_stat.f_iosize;
if (ap->a_bop != NULL)
*ap->a_bop = &vp->v_bufobj;
if (ap->a_bnp != NULL)
*ap->a_bnp = ap->a_bn * btodb(iosize);
if (ap->a_runp == NULL)
return (0);
tnp = VP_TO_TARFS_NODE(vp);
off = ap->a_bn * iosize;
ra = rb = 0;
for (u_int i = 0; i < tnp->nblk; i++) {
off_t bs, be;
bs = tnp->blk[i].o;
be = tnp->blk[i].o + tnp->blk[i].l;
if (off > be)
continue;
else if (off < bs) {
/* We're in a hole. */
ra = bs - off < iosize ?
0 : howmany(bs - (off + iosize), iosize);
rb = howmany(off - (i == 0 ?
0 : tnp->blk[i - 1].o + tnp->blk[i - 1].l),
iosize);
break;
} else {
/* We'll be reading from the backing file. */
ra = be - off < iosize ?
0 : howmany(be - (off + iosize), iosize);
rb = howmany(off - bs, iosize);
break;
}
}
rmax = vp->v_mount->mnt_iosize_max / iosize - 1;
*ap->a_runp = imin(ra, rmax);
if (ap->a_runb != NULL)
*ap->a_runb = imin(rb, rmax);
return (0);
}
static int
tarfs_getattr(struct vop_getattr_args *ap)
{
@ -629,6 +683,7 @@ struct vop_vector tarfs_vnodeops = {
.vop_default = &default_vnodeops,
.vop_access = tarfs_access,
.vop_bmap = tarfs_bmap,
.vop_cachedlookup = tarfs_lookup,
.vop_close = tarfs_close,
.vop_getattr = tarfs_getattr,