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csum-file: introduce sha1file_checkpoint

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It is useful to be able to rewind a check-summed file to a certain
previous state after writing data into it using sha1write() API. The
fast-import command does this after streaming a blob data to the packfile
being generated and then noticing that the same blob has already been
written, and it does this with a private code truncate_pack() that is
commented as "Yes, this is a layering violation".

Introduce two API functions, sha1file_checkpoint(), that allows the caller
to save a state of a sha1file, and then later revert it to the saved state.
Use it to reimplement truncate_pack().

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano
2011-11-17 16:26:54 -08:00
parent 0e990530ae
commit 6c52614864
3 changed files with 37 additions and 17 deletions
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20
csum-file.c
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@ -158,6 +158,26 @@ struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp
return f;
}
void sha1file_checkpoint(struct sha1file *f, struct sha1file_checkpoint *checkpoint)
{
sha1flush(f);
checkpoint->offset = f->total;
checkpoint->ctx = f->ctx;
}
int sha1file_truncate(struct sha1file *f, struct sha1file_checkpoint *checkpoint)
{
off_t offset = checkpoint->offset;
if (ftruncate(f->fd, offset) ||
lseek(f->fd, offset, SEEK_SET) != offset)
return -1;
f->total = offset;
f->ctx = checkpoint->ctx;
f->offset = 0; /* sha1flush() was called in checkpoint */
return 0;
}
void crc32_begin(struct sha1file *f)
{
f->crc32 = crc32(0, NULL, 0);