fs: Fix fallocate with zero-message-open
fs: Fix fallocate with zero-message-open

fallocate needs a writable fd so upgrade the fd if necessary.

BUG=b:180681350
TEST=`fallocate -p -o 1K -l 1K foo` works

Change-Id: I272e93539d82bec4c155cc924a59ba95baf2620d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2717903
Tested-by: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>
Auto-Submit: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-by: Stephen Barber <7719587e4b5a49340661b214ec85602f3918d06f@chromium.org>
Commit-Queue: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm