support: Fix detecting hole support on >2KB-block filesystems

When detecting hole support, we write at 16MiB, and filesystems will
typically need two levels of data to record that. On filesystems with
8KB block, the two indirection blocks will require a total of 16KB
overhead, thus 32 512-byte sectors.

Spotted on GNU/Hurd with a 4KB blocks filesystem, but also happens on Linux
with 4KB or 8KB blocks filesystems.

* support/support_descriptor_supports_holes.c
(support_descriptor_supports_holes): Set block_headroom to 32.
This commit is contained in:
Samuel Thibault 2020-06-04 20:52:19 +02:00
parent 6f10ff02cb
commit 3f6e4fc454

View File

@ -34,8 +34,10 @@ support_descriptor_supports_holes (int fd)
write_offset = 16 * 1024 * 1024,
/* Our write may add this number of additional blocks (see
block_limit below). */
block_headroom = 8,
block_limit below): writing at offset 16M can require two data block
indirections, each of which can be as large as 8KB on ext2, thus 32
512B sectors. */
block_headroom = 32,
};
struct stat64 st;