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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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9
csum-file.h
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@ -17,6 +17,15 @@ struct sha1file {
unsigned char buffer[8192];
};
/* Checkpoint */
struct sha1file_checkpoint {
off_t offset;
git_SHA_CTX ctx;
};
extern void sha1file_checkpoint(struct sha1file *, struct sha1file_checkpoint *);
extern int sha1file_truncate(struct sha1file *, struct sha1file_checkpoint *);
/* sha1close flags */
#define CSUM_CLOSE 1
#define CSUM_FSYNC 2