sparse-index: add 'sdir' index extension
The index format does not currently allow for sparse directory entries. This violates some expectations that older versions of Git or third-party tools might not understand. We need an indicator inside the index file to warn these tools to not interact with a sparse index unless they are aware of sparse directory entries. Add a new _required_ index extension, 'sdir', that indicates that the index may contain sparse directory entries. This allows us to continue to use the differences in index formats 2, 3, and 4 before we create a new index version 5 in a later change. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Derrick Stolee committed
Mar 30, 2021 at 13:10 UTC
cd42415fb4c9680f308ebf8f9f85ba90ae6014be
2 files changed
+21
Documentation/technical/index-format.txt
+12
@@ -392,3 +392,15 @@ The remaining data of each directory block is grouped by type:
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in this block of entries.
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- 32-bit count of cache entries in this block
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+
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+== Sparse Directory Entries
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+
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+ When using sparse-checkout in cone mode, some entire directories within
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+ the index can be summarized by pointing to a tree object instead of the
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+ entire expanded list of paths within that tree. An index containing such
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+ entries is a "sparse index". Index format versions 4 and less were not
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+ implemented with such entries in mind. Thus, for these versions, an
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+ index containing sparse directory entries will include this extension
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+ with signature { 's', 'd', 'i', 'r' }. Like the split-index extension,
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+ tools should avoid interacting with a sparse index unless they understand
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+ this extension.
read-cache.c
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@@ -47,6 +47,7 @@
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#define CACHE_EXT_FSMONITOR 0x46534D4E /* "FSMN" */
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#define CACHE_EXT_ENDOFINDEXENTRIES 0x454F4945 /* "EOIE" */
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#define CACHE_EXT_INDEXENTRYOFFSETTABLE 0x49454F54 /* "IEOT" */
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+#define CACHE_EXT_SPARSE_DIRECTORIES 0x73646972 /* "sdir" */
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/* changes that can be kept in $GIT_DIR/index (basically all extensions) */
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#define EXTMASK (RESOLVE_UNDO_CHANGED | CACHE_TREE_CHANGED | \
@@ -1763,6 +1764,10 @@ static int read_index_extension(struct index_state *istate,
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case CACHE_EXT_INDEXENTRYOFFSETTABLE:
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/* already handled in do_read_index() */
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break;
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+ case CACHE_EXT_SPARSE_DIRECTORIES:
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+ /* no content, only an indicator */
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+ istate->sparse_index = 1;
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+ break;
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default:
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if (*ext < 'A' || 'Z' < *ext)
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return error(_("index uses %.4s extension, which we do not understand"),
@@ -3020,6 +3025,10 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
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if (err)
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return -1;
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}
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+ if (istate->sparse_index) {
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+ if (write_index_ext_header(&c, &eoie_c, newfd, CACHE_EXT_SPARSE_DIRECTORIES, 0) < 0)
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+ return -1;
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+ }
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/*
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* CACHE_EXT_ENDOFINDEXENTRIES must be written as the last entry before the SHA1