setup_bdiff_cffi.py

vfs: use checkambigatclosing in checkambig=True but atomictemp=False case

In Mercurial source tree, opening a file in "a"/"a+" mode like below
doesn't specify atomictemp=True for vfs, and this avoids file stat
ambiguity check by atomictempfile.

  - writing changes out in revlog layer uses "a+" mode
  - truncation in repair.strip() uses "a" mode
  - truncation in transaction._playback() uses "a" mode

If steps below occurs at "the same time in sec", all of mtime, ctime
and size are same between (1) and (3).

  1. append data to revlog-style file (and close transaction)
  2. discard appended data by truncation (strip or rollback)
  3. append same size but different data to revlog-style file again

Therefore, cache validation doesn't work after (3) as expected.

This patch uses checkambigatclosing in checkambig=True but
atomictemp=False case, to check (and get rid of) file stat ambiguity
at closing.

This is a part of ExactCacheValidationPlan.

    https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

from __future__ import absolute_import

import cffi
import os

ffi = cffi.FFI()
ffi.set_source("_bdiff_cffi",
    open(os.path.join(os.path.join(os.path.dirname(__file__), 'mercurial'),
        'bdiff.c')).read(), include_dirs=['mercurial'])
ffi.cdef("""
struct bdiff_line {
    int hash, n, e;
    ssize_t len;
    const char *l;
};

struct bdiff_hunk;
struct bdiff_hunk {
    int a1, a2, b1, b2;
    struct bdiff_hunk *next;
};

int bdiff_splitlines(const char *a, ssize_t len, struct bdiff_line **lr);
int bdiff_diff(struct bdiff_line *a, int an, struct bdiff_line *b, int bn,
    struct bdiff_hunk *base);
void bdiff_freehunks(struct bdiff_hunk *l);
void free(void*);
""")

if __name__ == '__main__':
    ffi.compile()