On Tue, Jul 30, 2024 at 07:03:50PM +0200, Florian Weimer wrote: > > The only relevant exception is probably ext4 in ext2/ext3 mode, where > > the latter might still have users left running real workloads on it > > and not using it for usb disks or VM images. > > Why doesn't the kernel perform allocation in these cases? There doesn't > seem to be a file-system-specific reason why it's impossible to do. Because in general it's a really stupid idea. You don't get a better allocation patter, but you are writing every block twice, making things significantly slower and wearing the device out in the process if it is flash based. > At the very least, we should have a variant of ftruncate that never > truncates, likely under the fallocate umbrella. It seems that that's > how posix_fallocate is used sometimes, for avoiding SIGBUS with mmap. > To these use cases, whether extents are allocated or not does not > matter. I don't see how that is related. > If we removed the fallback code from glibc today, it would just be > EOPNOTSUPP that leaks to applications, so it's structurally the same > issue. Not really. EOPNOTSUPP is a valid error code, that has historically been returned by other operating systems and even other libc implementations for Linux
