index-format.txt: document SHA-256 index format
Document that in SHA-1 repositories, we use SHA-1 and in SHA-256 repositories, we use SHA-256, then replace all other uses of "SHA-1" with something more neutral. Avoid referring to "160-bit" hash values. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Martin Ågren committed
Aug 15, 2020 at 18:06 UTC
123712ba41164146cd711dab6fe107b62d443f12
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Documentation/technical/index-format.txt
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@@ -3,8 +3,11 @@ Git index format
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== The Git index file has the following format
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- All binary numbers are in network byte order. Version 2 is described
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- here unless stated otherwise.
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+ All binary numbers are in network byte order.
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+ In a repository using the traditional SHA-1, checksums and object IDs
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+ (object names) mentioned below are all computed using SHA-1. Similarly,
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+ in SHA-256 repositories, these values are computed using SHA-256.
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+ Version 2 is described here unless stated otherwise.
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- A 12-byte header consisting of
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@@ -32,8 +35,7 @@ Git index format
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Extension data
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- - 160-bit SHA-1 over the content of the index file before this
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- checksum.
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+ - Hash checksum over the content of the index file before this checksum.
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== Index entry
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@@ -80,7 +82,7 @@ Git index format
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32-bit file size
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This is the on-disk size from stat(2), truncated to 32-bit.
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- 160-bit SHA-1 for the represented object
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+ Object name for the represented object
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A 16-bit 'flags' field split into (high to low bits)
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@@ -160,8 +162,8 @@ Git index format
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- A newline (ASCII 10); and
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- - 160-bit object name for the object that would result from writing
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- this span of index as a tree.
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+ - Object name for the object that would result from writing this span
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+ of index as a tree.
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An entry can be in an invalidated state and is represented by having
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a negative number in the entry_count field. In this case, there is no
@@ -198,7 +200,7 @@ Git index format
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stage 1 to 3 (a missing stage is represented by "0" in this field);
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and
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- - At most three 160-bit object names of the entry in stages from 1 to 3
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+ - At most three object names of the entry in stages from 1 to 3
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(nothing is written for a missing stage).
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=== Split index
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The extension consists of:
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- - 160-bit SHA-1 of the shared index file. The shared index file path
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- is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the
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+ - Hash of the shared index file. The shared index file path
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+ is $GIT_DIR/sharedindex.<hash>. If all bits are zero, the
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index does not require a shared index file.
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- An ewah-encoded delete bitmap, each bit represents an entry in the
@@ -253,10 +255,10 @@ Git index format
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- 32-bit dir_flags (see struct dir_struct)
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- - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
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+ - Hash of $GIT_DIR/info/exclude. A null hash means the file
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does not exist.
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- - 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does
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+ - Hash of core.excludesfile. A null hash means the file does
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not exist.
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- NUL-terminated string of per-dir exclude file name. This usually
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- An ewah bitmap, the n-th bit records "check-only" bit of
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read_directory_recursive() for the n-th directory.
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- - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
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+ - An ewah bitmap, the n-th bit indicates whether hash and stat data
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is valid for the n-th directory and exists in the next data.
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- An array of stat data. The n-th data corresponds with the n-th
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"one" bit in the previous ewah bitmap.
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- - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
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+ - An array of hashes. The n-th hash corresponds with the n-th "one" bit
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in the previous ewah bitmap.
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- One NUL.
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- 32-bit offset to the end of the index entries
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- - 160-bit SHA-1 over the extension types and their sizes (but not
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+ - Hash over the extension types and their sizes (but not
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their contents). E.g. if we have "TREE" extension that is N-bytes
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long, "REUC" extension that is M-bytes long, followed by "EOIE",
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then the hash would be:
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- SHA-1("TREE" + <binary representation of N> +
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+ Hash("TREE" + <binary representation of N> +
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"REUC" + <binary representation of M>)
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== Index Entry Offset Table