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loop-util: work around cache invalidation bug in older kernels

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Inspired by the discussions in #21003.

Inspired in particular by what Android apexd does:

https://android.googlesource.com/platform/system/apex/+/refs/heads/master/apexd/apexd_loop.cpp
This commit is contained in:
Lennart Poettering 2021-10-18 22:34:54 +02:00
parent e8c7c4d9d1
commit b9a9748abc
1 changed files with 15 additions and 0 deletions
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15
src/shared/loop-util.c
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@ -326,6 +326,21 @@ static int loop_configure(
random_u64_range(UINT64_C(240) * USEC_PER_MSEC * n_attempts/64));
}
/* Work around a kernel bug, where changing offset/size of the loopback device doesn't correctly
* invalidate the buffer cache. For details see:
*
* https://android.googlesource.com/platform/system/apex/+/bef74542fbbb4cd629793f4efee8e0053b360570
*
* This was fixed in kernel 5.0, see:
*
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5db470e229e22b7eda6e23b5566e532c96fb5bc3
*
* We'll run the work-around here in the legacy LOOP_SET_STATUS64 codepath. In the LOOP_CONFIGURE
* codepath above it should not be necessary. */
if (c->info.lo_offset != 0 || c->info.lo_sizelimit != 0)
if (ioctl(fd, BLKFLSBUF, 0) < 0)
log_debug_errno(errno, "Failed to issue BLKFLSBUF ioctl, ignoring: %m");
/* LO_FLAGS_DIRECT_IO is a flags we need to configure via explicit ioctls. */
if (FLAGS_SET(c->info.lo_flags, LO_FLAGS_DIRECT_IO)) {
unsigned long b = 1;