Module Name: src
Committed By: riastradh
Date: Sat Mar 21 06:11:05 UTC 2020
Modified Files:
src/sys/ufs/lfs: lfs.h lfs_accessors.h
Log Message:
Avoid misaligned access to lfs64 on-disk records in memory.
lfs64 directory entries are only 32-bit aligned in order to conserve
space in directory blocks, and we had a hack to stuff a 64-bit inode
in them. This replaces the hack by __aligned(4) __packed, and goes
further:
1. It's not clear that all the other lfs64 data structures are 64-bit
aligned on disk to begin with. We can go through these later and
upgrade them from
struct foo64 {
...
} __aligned(4) __packed;
union foo {
struct foo64 f64;
...
};
to
struct foo64 {
...
};
union foo {
struct foo64 f64 __aligned(8);
...
} __aligned(4) __packed;
if we really want to take advantage of 64-bit memory accesses.
However, the __aligned(4) __packed must remain on the union
because:
2. We access even the lfs32 data structures via a union that has
lfs64 members, and it turns out that compilers will assume access
through a union with 64-bit aligned members implies the whole
union has 64-bit alignment, even if we're only accessing a 32-bit
aligned member.
To generate a diff of this commit:
cvs rdiff -u -r1.206 -r1.207 src/sys/ufs/lfs/lfs.h
cvs rdiff -u -r1.48 -r1.49 src/sys/ufs/lfs/lfs_accessors.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
