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git/csum-file.h

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git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
#ifndef CSUM_FILE_H
#define CSUM_FILE_H
add throughput display to git-push This one triggers only when git-pack-objects is called with --all-progress and --stdout which is the combination used by git-push. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 22:06:21 +01:00
struct progress;
git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
/* A SHA1-protected file */
struct sha1file {
remove dead code from the csum-file interface The provided name argument is always constant and valid in every caller's context, so no need to have an array of PATH_MAX chars to copy it into when a simple pointer will do. Unfortunately that means getting rid of wascally wabbits too. The 'error' field is also unused. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-05 04:54:50 +01:00
int fd;
unsigned int offset;
git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
SHA_CTX ctx;
make display of total transferred more accurate The throughput display needs a delay period before accounting and displaying anything. Yet it might be called after some amount of data has already been transferred. The display of total data is therefore accounted late and therefore smaller than the reality. Let's call display_throughput() with an absolute amount of transferred data instead of a relative number, and let the throughput code find the relative amount of data by itself as needed. This way the displayed total is always exact. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-05 04:15:41 +01:00
off_t total;
add throughput display to git-push This one triggers only when git-pack-objects is called with --all-progress and --stdout which is the combination used by git-push. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 22:06:21 +01:00
struct progress *tp;
remove dead code from the csum-file interface The provided name argument is always constant and valid in every caller's context, so no need to have an array of PATH_MAX chars to copy it into when a simple pointer will do. Unfortunately that means getting rid of wascally wabbits too. The 'error' field is also unused. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-05 04:54:50 +01:00
const char *name;
compute a CRC32 for each object as stored in a pack The most important optimization for performance when repacking is the ability to reuse data from a previous pack as is and bypass any delta or even SHA1 computation by simply copying the raw data from one pack to another directly. The problem with this is that any data corruption within a copied object would go unnoticed and the new (repacked) pack would be self-consistent with its own checksum despite containing a corrupted object. This is a real issue that already happened at least once in the past. In some attempt to prevent this, we validate the copied data by inflating it and making sure no error is signaled by zlib. But this is still not perfect as a significant portion of a pack content is made of object headers and references to delta base objects which are not deflated and therefore not validated when repacking actually making the pack data reuse still not as safe as it could be. Of course a full SHA1 validation could be performed, but that implies full data inflating and delta replaying which is extremely costly, which cost the data reuse optimization was designed to avoid in the first place. So the best solution to this is simply to store a CRC32 of the raw pack data for each object in the pack index. This way any object in a pack can be validated before being copied as is in another pack, including header and any other non deflated data. Why CRC32 instead of a faster checksum like Adler32? Quoting Wikipedia: Jonathan Stone discovered in 2001 that Adler-32 has a weakness for very short messages. He wrote "Briefly, the problem is that, for very short packets, Adler32 is guaranteed to give poor coverage of the available bits. Don't take my word for it, ask Mark Adler. :-)" The problem is that sum A does not wrap for short messages. The maximum value of A for a 128-byte message is 32640, which is below the value 65521 used by the modulo operation. An extended explanation can be found in RFC 3309, which mandates the use of CRC32 instead of Adler-32 for SCTP, the Stream Control Transmission Protocol. In the context of a GIT pack, we have lots of small objects, especially deltas, which are likely to be quite small and in a size range for which Adler32 is dimed not to be sufficient. Another advantage of CRC32 is the possibility for recovery from certain types of small corruptions like single bit errors which are the most probable type of corruptions. OK what this patch does is to compute the CRC32 of each object written to a pack within pack-objects. It is not written to the index yet and it is obviously not validated when reusing pack data yet either. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-04-09 07:06:31 +02:00
int do_crc;
uint32_t crc32;
git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
unsigned char buffer[8192];
};
csum-file: add "sha1fd()" to create a SHA1 csum file from an existing file descriptor We'll use this soon to write pack-files to stdout.
2005-06-28 20:10:06 +02:00
extern struct sha1file *sha1fd(int fd, const char *name);
add throughput display to git-push This one triggers only when git-pack-objects is called with --all-progress and --stdout which is the combination used by git-push. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 22:06:21 +01:00
extern struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp);
csum-file interface updates: return resulting SHA1 Also, make the writing of the SHA1 as a end-header be conditional: not every user will necessarily want to write the SHA1 to the file itself, even though current users do (but we migh end up using the same helper functions for the object files themselves, that don't do this). This also makes the packed index file contain the SHA1 of the packed data file at the end (just before its own SHA1). That way you can validate the pairing of the two if you want to.
2005-06-27 07:01:46 +02:00
extern int sha1close(struct sha1file *, unsigned char *, int);
git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
extern int sha1write(struct sha1file *, void *, unsigned int);
compute a CRC32 for each object as stored in a pack The most important optimization for performance when repacking is the ability to reuse data from a previous pack as is and bypass any delta or even SHA1 computation by simply copying the raw data from one pack to another directly. The problem with this is that any data corruption within a copied object would go unnoticed and the new (repacked) pack would be self-consistent with its own checksum despite containing a corrupted object. This is a real issue that already happened at least once in the past. In some attempt to prevent this, we validate the copied data by inflating it and making sure no error is signaled by zlib. But this is still not perfect as a significant portion of a pack content is made of object headers and references to delta base objects which are not deflated and therefore not validated when repacking actually making the pack data reuse still not as safe as it could be. Of course a full SHA1 validation could be performed, but that implies full data inflating and delta replaying which is extremely costly, which cost the data reuse optimization was designed to avoid in the first place. So the best solution to this is simply to store a CRC32 of the raw pack data for each object in the pack index. This way any object in a pack can be validated before being copied as is in another pack, including header and any other non deflated data. Why CRC32 instead of a faster checksum like Adler32? Quoting Wikipedia: Jonathan Stone discovered in 2001 that Adler-32 has a weakness for very short messages. He wrote "Briefly, the problem is that, for very short packets, Adler32 is guaranteed to give poor coverage of the available bits. Don't take my word for it, ask Mark Adler. :-)" The problem is that sum A does not wrap for short messages. The maximum value of A for a 128-byte message is 32640, which is below the value 65521 used by the modulo operation. An extended explanation can be found in RFC 3309, which mandates the use of CRC32 instead of Adler-32 for SCTP, the Stream Control Transmission Protocol. In the context of a GIT pack, we have lots of small objects, especially deltas, which are likely to be quite small and in a size range for which Adler32 is dimed not to be sufficient. Another advantage of CRC32 is the possibility for recovery from certain types of small corruptions like single bit errors which are the most probable type of corruptions. OK what this patch does is to compute the CRC32 of each object written to a pack within pack-objects. It is not written to the index yet and it is obviously not validated when reusing pack data yet either. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-04-09 07:06:31 +02:00
extern void crc32_begin(struct sha1file *);
extern uint32_t crc32_end(struct sha1file *);
git-pack-objects: write the pack files with a SHA1 csum We want to be able to check their integrity later, and putting the sha1-sum of the contents at the end is a good thing. The writing routines are generic, so we could try to re-use them for the index file, instead of having the same logic duplicated. Update unpack-objects to know about the extra 20 bytes at the end of the index.
2005-06-27 05:27:56 +02:00
#endif
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