Merge branch 'tg/maint-cache-name-compare' into maint
[git/git.git] / read-cache.c
index 0cd13aa..b645827 100644 (file)
@@ -12,6 +12,8 @@
 #include "commit.h"
 #include "blob.h"
 #include "resolve-undo.h"
+#include "strbuf.h"
+#include "varint.h"
 
 static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int really);
 
@@ -92,7 +94,7 @@ static int ce_compare_data(struct cache_entry *ce, struct stat *st)
 
        if (fd >= 0) {
                unsigned char sha1[20];
-               if (!index_fd(sha1, fd, st, 0, OBJ_BLOB, ce->name))
+               if (!index_fd(sha1, fd, st, OBJ_BLOB, ce->name, 0))
                        match = hashcmp(sha1, ce->sha1);
                /* index_fd() closed the file descriptor already */
        }
@@ -157,16 +159,6 @@ static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
        return 0;
 }
 
-static int is_empty_blob_sha1(const unsigned char *sha1)
-{
-       static const unsigned char empty_blob_sha1[20] = {
-               0xe6,0x9d,0xe2,0x9b,0xb2,0xd1,0xd6,0x43,0x4b,0x8b,
-               0x29,0xae,0x77,0x5a,0xd8,0xc2,0xe4,0x8c,0x53,0x91
-       };
-
-       return !hashcmp(sha1, empty_blob_sha1);
-}
-
 static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
 {
        unsigned int changed = 0;
@@ -613,6 +605,29 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
                ce->ce_mode = ce_mode_from_stat(ent, st_mode);
        }
 
+       /* When core.ignorecase=true, determine if a directory of the same name but differing
+        * case already exists within the Git repository.  If it does, ensure the directory
+        * case of the file being added to the repository matches (is folded into) the existing
+        * entry's directory case.
+        */
+       if (ignore_case) {
+               const char *startPtr = ce->name;
+               const char *ptr = startPtr;
+               while (*ptr) {
+                       while (*ptr && *ptr != '/')
+                               ++ptr;
+                       if (*ptr == '/') {
+                               struct cache_entry *foundce;
+                               ++ptr;
+                               foundce = index_name_exists(&the_index, ce->name, ptr - ce->name, ignore_case);
+                               if (foundce) {
+                                       memcpy((void *)startPtr, foundce->name + (startPtr - ce->name), ptr - startPtr);
+                                       startPtr = ptr;
+                               }
+                       }
+               }
+       }
+
        alias = index_name_exists(istate, ce->name, ce_namelen(ce), ignore_case);
        if (alias && !ce_stage(alias) && !ie_match_stat(istate, alias, st, ce_option)) {
                /* Nothing changed, really */
@@ -623,7 +638,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
                return 0;
        }
        if (!intent_only) {
-               if (index_path(ce->sha1, path, st, 1))
+               if (index_path(ce->sha1, path, st, HASH_WRITE_OBJECT))
                        return error("unable to index file %s", path);
        } else
                record_intent_to_add(ce);
@@ -688,30 +703,9 @@ int ce_same_name(struct cache_entry *a, struct cache_entry *b)
        return ce_namelen(b) == len && !memcmp(a->name, b->name, len);
 }
 
-int ce_path_match(const struct cache_entry *ce, const char **pathspec)
+int ce_path_match(const struct cache_entry *ce, const struct pathspec *pathspec)
 {
-       const char *match, *name;
-       int len;
-
-       if (!pathspec)
-               return 1;
-
-       len = ce_namelen(ce);
-       name = ce->name;
-       while ((match = *pathspec++) != NULL) {
-               int matchlen = strlen(match);
-               if (matchlen > len)
-                       continue;
-               if (memcmp(name, match, matchlen))
-                       continue;
-               if (matchlen && name[matchlen-1] == '/')
-                       return 1;
-               if (name[matchlen] == '/' || !name[matchlen])
-                       return 1;
-               if (!matchlen)
-                       return 1;
-       }
-       return 0;
+       return match_pathspec_depth(pathspec, ce->name, ce_namelen(ce), 0, NULL);
 }
 
 /*
@@ -729,11 +723,12 @@ static int verify_dotfile(const char *rest)
         * has already been discarded, we now test
         * the rest.
         */
-       switch (*rest) {
+
        /* "." is not allowed */
-       case '\0': case '/':
+       if (*rest == '\0' || is_dir_sep(*rest))
                return 0;
 
+       switch (*rest) {
        /*
         * ".git" followed by  NUL or slash is bad. This
         * shares the path end test with the ".." case.
@@ -746,7 +741,7 @@ static int verify_dotfile(const char *rest)
                rest += 2;
        /* fallthrough */
        case '.':
-               if (rest[1] == '\0' || rest[1] == '/')
+               if (rest[1] == '\0' || is_dir_sep(rest[1]))
                        return 0;
        }
        return 1;
@@ -756,23 +751,19 @@ int verify_path(const char *path)
 {
        char c;
 
+       if (has_dos_drive_prefix(path))
+               return 0;
+
        goto inside;
        for (;;) {
                if (!c)
                        return 1;
-               if (c == '/') {
+               if (is_dir_sep(c)) {
 inside:
                        c = *path++;
-                       switch (c) {
-                       default:
-                               continue;
-                       case '/': case '\0':
-                               break;
-                       case '.':
-                               if (verify_dotfile(path))
-                                       continue;
-                       }
-                       return 0;
+                       if ((c == '.' && !verify_dotfile(path)) ||
+                           is_dir_sep(c) || c == '\0')
+                               return 0;
                }
                c = *path++;
        }
@@ -1007,7 +998,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
  */
 static struct cache_entry *refresh_cache_ent(struct index_state *istate,
                                             struct cache_entry *ce,
-                                            unsigned int options, int *err)
+                                            unsigned int options, int *err,
+                                            int *changed_ret)
 {
        struct stat st;
        struct cache_entry *updated;
@@ -1039,6 +1031,8 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
        }
 
        changed = ie_match_stat(istate, ce, &st, options);
+       if (changed_ret)
+               *changed_ret = changed;
        if (!changed) {
                /*
                 * The path is unchanged.  If we were told to ignore
@@ -1086,17 +1080,17 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 }
 
 static void show_file(const char * fmt, const char * name, int in_porcelain,
-                     int * first, char *header_msg)
+                     int * first, const char *header_msg)
 {
        if (in_porcelain && *first && header_msg) {
                printf("%s\n", header_msg);
-               *first=0;
+               *first = 0;
        }
        printf(fmt, name);
 }
 
 int refresh_index(struct index_state *istate, unsigned int flags, const char **pathspec,
-                 char *seen, char *header_msg)
+                 char *seen, const char *header_msg)
 {
        int i;
        int has_errors = 0;
@@ -1108,19 +1102,31 @@ int refresh_index(struct index_state *istate, unsigned int flags, const char **p
        int first = 1;
        int in_porcelain = (flags & REFRESH_IN_PORCELAIN);
        unsigned int options = really ? CE_MATCH_IGNORE_VALID : 0;
-       const char *needs_update_fmt;
-       const char *needs_merge_fmt;
-
-       needs_update_fmt = (in_porcelain ? "M\t%s\n" : "%s: needs update\n");
-       needs_merge_fmt = (in_porcelain ? "U\t%s\n" : "%s: needs merge\n");
+       const char *modified_fmt;
+       const char *deleted_fmt;
+       const char *typechange_fmt;
+       const char *added_fmt;
+       const char *unmerged_fmt;
+
+       modified_fmt = (in_porcelain ? "M\t%s\n" : "%s: needs update\n");
+       deleted_fmt = (in_porcelain ? "D\t%s\n" : "%s: needs update\n");
+       typechange_fmt = (in_porcelain ? "T\t%s\n" : "%s needs update\n");
+       added_fmt = (in_porcelain ? "A\t%s\n" : "%s needs update\n");
+       unmerged_fmt = (in_porcelain ? "U\t%s\n" : "%s: needs merge\n");
        for (i = 0; i < istate->cache_nr; i++) {
                struct cache_entry *ce, *new;
                int cache_errno = 0;
+               int changed = 0;
+               int filtered = 0;
 
                ce = istate->cache[i];
                if (ignore_submodules && S_ISGITLINK(ce->ce_mode))
                        continue;
 
+               if (pathspec &&
+                   !match_pathspec(pathspec, ce->name, strlen(ce->name), 0, seen))
+                       filtered = 1;
+
                if (ce_stage(ce)) {
                        while ((i < istate->cache_nr) &&
                               ! strcmp(istate->cache[i]->name, ce->name))
@@ -1128,18 +1134,22 @@ int refresh_index(struct index_state *istate, unsigned int flags, const char **p
                        i--;
                        if (allow_unmerged)
                                continue;
-                       show_file(needs_merge_fmt, ce->name, in_porcelain, &first, header_msg);
+                       if (!filtered)
+                               show_file(unmerged_fmt, ce->name, in_porcelain,
+                                         &first, header_msg);
                        has_errors = 1;
                        continue;
                }
 
-               if (pathspec && !match_pathspec(pathspec, ce->name, strlen(ce->name), 0, seen))
+               if (filtered)
                        continue;
 
-               new = refresh_cache_ent(istate, ce, options, &cache_errno);
+               new = refresh_cache_ent(istate, ce, options, &cache_errno, &changed);
                if (new == ce)
                        continue;
                if (!new) {
+                       const char *fmt;
+
                        if (not_new && cache_errno == ENOENT)
                                continue;
                        if (really && cache_errno == EINVAL) {
@@ -1151,7 +1161,17 @@ int refresh_index(struct index_state *istate, unsigned int flags, const char **p
                        }
                        if (quiet)
                                continue;
-                       show_file(needs_update_fmt, ce->name, in_porcelain, &first, header_msg);
+
+                       if (cache_errno == ENOENT)
+                               fmt = deleted_fmt;
+                       else if (ce->ce_flags & CE_INTENT_TO_ADD)
+                               fmt = added_fmt; /* must be before other checks */
+                       else if (changed & TYPE_CHANGED)
+                               fmt = typechange_fmt;
+                       else
+                               fmt = modified_fmt;
+                       show_file(fmt,
+                                 ce->name, in_porcelain, &first, header_msg);
                        has_errors = 1;
                        continue;
                }
@@ -1163,18 +1183,77 @@ int refresh_index(struct index_state *istate, unsigned int flags, const char **p
 
 static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int really)
 {
-       return refresh_cache_ent(&the_index, ce, really, NULL);
+       return refresh_cache_ent(&the_index, ce, really, NULL, NULL);
 }
 
+
+/*****************************************************************
+ * Index File I/O
+ *****************************************************************/
+
+#define INDEX_FORMAT_DEFAULT 3
+
+/*
+ * dev/ino/uid/gid/size are also just tracked to the low 32 bits
+ * Again - this is just a (very strong in practice) heuristic that
+ * the inode hasn't changed.
+ *
+ * We save the fields in big-endian order to allow using the
+ * index file over NFS transparently.
+ */
+struct ondisk_cache_entry {
+       struct cache_time ctime;
+       struct cache_time mtime;
+       unsigned int dev;
+       unsigned int ino;
+       unsigned int mode;
+       unsigned int uid;
+       unsigned int gid;
+       unsigned int size;
+       unsigned char sha1[20];
+       unsigned short flags;
+       char name[FLEX_ARRAY]; /* more */
+};
+
+/*
+ * This struct is used when CE_EXTENDED bit is 1
+ * The struct must match ondisk_cache_entry exactly from
+ * ctime till flags
+ */
+struct ondisk_cache_entry_extended {
+       struct cache_time ctime;
+       struct cache_time mtime;
+       unsigned int dev;
+       unsigned int ino;
+       unsigned int mode;
+       unsigned int uid;
+       unsigned int gid;
+       unsigned int size;
+       unsigned char sha1[20];
+       unsigned short flags;
+       unsigned short flags2;
+       char name[FLEX_ARRAY]; /* more */
+};
+
+/* These are only used for v3 or lower */
+#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
+#define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len)
+#define ondisk_cache_entry_extended_size(len) align_flex_name(ondisk_cache_entry_extended,len)
+#define ondisk_ce_size(ce) (((ce)->ce_flags & CE_EXTENDED) ? \
+                           ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
+                           ondisk_cache_entry_size(ce_namelen(ce)))
+
 static int verify_hdr(struct cache_header *hdr, unsigned long size)
 {
        git_SHA_CTX c;
        unsigned char sha1[20];
+       int hdr_version;
 
        if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
                return error("bad signature");
-       if (hdr->hdr_version != htonl(2) && hdr->hdr_version != htonl(3))
-               return error("bad index version");
+       hdr_version = ntohl(hdr->hdr_version);
+       if (hdr_version < 2 || 4 < hdr_version)
+               return error("bad index version %d", hdr_version);
        git_SHA1_Init(&c);
        git_SHA1_Update(&c, hdr, size - 20);
        git_SHA1_Final(sha1, &c);
@@ -1208,63 +1287,115 @@ int read_index(struct index_state *istate)
        return read_index_from(istate, get_index_file());
 }
 
-static void convert_from_disk(struct ondisk_cache_entry *ondisk, struct cache_entry *ce)
+#ifndef NEEDS_ALIGNED_ACCESS
+#define ntoh_s(var) ntohs(var)
+#define ntoh_l(var) ntohl(var)
+#else
+static inline uint16_t ntoh_s_force_align(void *p)
+{
+       uint16_t x;
+       memcpy(&x, p, sizeof(x));
+       return ntohs(x);
+}
+static inline uint32_t ntoh_l_force_align(void *p)
+{
+       uint32_t x;
+       memcpy(&x, p, sizeof(x));
+       return ntohl(x);
+}
+#define ntoh_s(var) ntoh_s_force_align(&(var))
+#define ntoh_l(var) ntoh_l_force_align(&(var))
+#endif
+
+static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
+                                                  unsigned int flags,
+                                                  const char *name,
+                                                  size_t len)
+{
+       struct cache_entry *ce = xmalloc(cache_entry_size(len));
+
+       ce->ce_ctime.sec = ntoh_l(ondisk->ctime.sec);
+       ce->ce_mtime.sec = ntoh_l(ondisk->mtime.sec);
+       ce->ce_ctime.nsec = ntoh_l(ondisk->ctime.nsec);
+       ce->ce_mtime.nsec = ntoh_l(ondisk->mtime.nsec);
+       ce->ce_dev   = ntoh_l(ondisk->dev);
+       ce->ce_ino   = ntoh_l(ondisk->ino);
+       ce->ce_mode  = ntoh_l(ondisk->mode);
+       ce->ce_uid   = ntoh_l(ondisk->uid);
+       ce->ce_gid   = ntoh_l(ondisk->gid);
+       ce->ce_size  = ntoh_l(ondisk->size);
+       ce->ce_flags = flags;
+       hashcpy(ce->sha1, ondisk->sha1);
+       memcpy(ce->name, name, len);
+       ce->name[len] = '\0';
+       return ce;
+}
+
+/*
+ * Adjacent cache entries tend to share the leading paths, so it makes
+ * sense to only store the differences in later entries.  In the v4
+ * on-disk format of the index, each on-disk cache entry stores the
+ * number of bytes to be stripped from the end of the previous name,
+ * and the bytes to append to the result, to come up with its name.
+ */
+static unsigned long expand_name_field(struct strbuf *name, const char *cp_)
+{
+       const unsigned char *ep, *cp = (const unsigned char *)cp_;
+       size_t len = decode_varint(&cp);
+
+       if (name->len < len)
+               die("malformed name field in the index");
+       strbuf_remove(name, name->len - len, len);
+       for (ep = cp; *ep; ep++)
+               ; /* find the end */
+       strbuf_add(name, cp, ep - cp);
+       return (const char *)ep + 1 - cp_;
+}
+
+static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk,
+                                           unsigned long *ent_size,
+                                           struct strbuf *previous_name)
 {
+       struct cache_entry *ce;
        size_t len;
        const char *name;
+       unsigned int flags;
 
-       ce->ce_ctime.sec = ntohl(ondisk->ctime.sec);
-       ce->ce_mtime.sec = ntohl(ondisk->mtime.sec);
-       ce->ce_ctime.nsec = ntohl(ondisk->ctime.nsec);
-       ce->ce_mtime.nsec = ntohl(ondisk->mtime.nsec);
-       ce->ce_dev   = ntohl(ondisk->dev);
-       ce->ce_ino   = ntohl(ondisk->ino);
-       ce->ce_mode  = ntohl(ondisk->mode);
-       ce->ce_uid   = ntohl(ondisk->uid);
-       ce->ce_gid   = ntohl(ondisk->gid);
-       ce->ce_size  = ntohl(ondisk->size);
        /* On-disk flags are just 16 bits */
-       ce->ce_flags = ntohs(ondisk->flags);
-
-       hashcpy(ce->sha1, ondisk->sha1);
-
-       len = ce->ce_flags & CE_NAMEMASK;
+       flags = ntoh_s(ondisk->flags);
+       len = flags & CE_NAMEMASK;
 
-       if (ce->ce_flags & CE_EXTENDED) {
+       if (flags & CE_EXTENDED) {
                struct ondisk_cache_entry_extended *ondisk2;
                int extended_flags;
                ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
-               extended_flags = ntohs(ondisk2->flags2) << 16;
+               extended_flags = ntoh_s(ondisk2->flags2) << 16;
                /* We do not yet understand any bit out of CE_EXTENDED_FLAGS */
                if (extended_flags & ~CE_EXTENDED_FLAGS)
                        die("Unknown index entry format %08x", extended_flags);
-               ce->ce_flags |= extended_flags;
+               flags |= extended_flags;
                name = ondisk2->name;
        }
        else
                name = ondisk->name;
 
-       if (len == CE_NAMEMASK)
-               len = strlen(name);
-       /*
-        * NEEDSWORK: If the original index is crafted, this copy could
-        * go unchecked.
-        */
-       memcpy(ce->name, name, len + 1);
-}
-
-static inline size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
-{
-       long per_entry;
-
-       per_entry = sizeof(struct cache_entry) - sizeof(struct ondisk_cache_entry);
-
-       /*
-        * Alignment can cause differences. This should be "alignof", but
-        * since that's a gcc'ism, just use the size of a pointer.
-        */
-       per_entry += sizeof(void *);
-       return ondisk_size + entries*per_entry;
+       if (!previous_name) {
+               /* v3 and earlier */
+               if (len == CE_NAMEMASK)
+                       len = strlen(name);
+               ce = cache_entry_from_ondisk(ondisk, flags, name, len);
+
+               *ent_size = ondisk_ce_size(ce);
+       } else {
+               unsigned long consumed;
+               consumed = expand_name_field(previous_name, name);
+               ce = cache_entry_from_ondisk(ondisk, flags,
+                                            previous_name->buf,
+                                            previous_name->len);
+
+               *ent_size = (name - ((char *)ondisk)) + consumed;
+       }
+       return ce;
 }
 
 /* remember to discard_cache() before reading a different cache! */
@@ -1272,10 +1403,11 @@ int read_index_from(struct index_state *istate, const char *path)
 {
        int fd, i;
        struct stat st;
-       unsigned long src_offset, dst_offset;
+       unsigned long src_offset;
        struct cache_header *hdr;
        void *mmap;
        size_t mmap_size;
+       struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
 
        errno = EBUSY;
        if (istate->initialized)
@@ -1308,33 +1440,30 @@ int read_index_from(struct index_state *istate, const char *path)
        if (verify_hdr(hdr, mmap_size) < 0)
                goto unmap;
 
+       istate->version = ntohl(hdr->hdr_version);
        istate->cache_nr = ntohl(hdr->hdr_entries);
        istate->cache_alloc = alloc_nr(istate->cache_nr);
        istate->cache = xcalloc(istate->cache_alloc, sizeof(struct cache_entry *));
-
-       /*
-        * The disk format is actually larger than the in-memory format,
-        * due to space for nsec etc, so even though the in-memory one
-        * has room for a few  more flags, we can allocate using the same
-        * index size
-        */
-       istate->alloc = xmalloc(estimate_cache_size(mmap_size, istate->cache_nr));
        istate->initialized = 1;
 
+       if (istate->version == 4)
+               previous_name = &previous_name_buf;
+       else
+               previous_name = NULL;
+
        src_offset = sizeof(*hdr);
-       dst_offset = 0;
        for (i = 0; i < istate->cache_nr; i++) {
                struct ondisk_cache_entry *disk_ce;
                struct cache_entry *ce;
+               unsigned long consumed;
 
                disk_ce = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
-               ce = (struct cache_entry *)((char *)istate->alloc + dst_offset);
-               convert_from_disk(disk_ce, ce);
+               ce = create_from_disk(disk_ce, &consumed, previous_name);
                set_index_entry(istate, i, ce);
 
-               src_offset += ondisk_ce_size(ce);
-               dst_offset += ce_size(ce);
+               src_offset += consumed;
        }
+       strbuf_release(&previous_name_buf);
        istate->timestamp.sec = st.st_mtime;
        istate->timestamp.nsec = ST_MTIME_NSEC(st);
 
@@ -1367,11 +1496,15 @@ unmap:
 
 int is_index_unborn(struct index_state *istate)
 {
-       return (!istate->cache_nr && !istate->alloc && !istate->timestamp.sec);
+       return (!istate->cache_nr && !istate->timestamp.sec);
 }
 
 int discard_index(struct index_state *istate)
 {
+       int i;
+
+       for (i = 0; i < istate->cache_nr; i++)
+               free(istate->cache[i]);
        resolve_undo_clear_index(istate);
        istate->cache_nr = 0;
        istate->cache_changed = 0;
@@ -1380,8 +1513,6 @@ int discard_index(struct index_state *istate)
        istate->name_hash_initialized = 0;
        free_hash(&istate->name_hash);
        cache_tree_free(&(istate->cache_tree));
-       free(istate->alloc);
-       istate->alloc = NULL;
        istate->initialized = 0;
 
        /* no need to throw away allocated active_cache */
@@ -1516,12 +1647,10 @@ static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
        }
 }
 
-static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
+/* Copy miscellaneous fields but not the name */
+static char *copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
+                                      struct cache_entry *ce)
 {
-       int size = ondisk_ce_size(ce);
-       struct ondisk_cache_entry *ondisk = xcalloc(1, size);
-       char *name;
-
        ondisk->ctime.sec = htonl(ce->ce_ctime.sec);
        ondisk->mtime.sec = htonl(ce->ce_mtime.sec);
        ondisk->ctime.nsec = htonl(ce->ce_ctime.nsec);
@@ -1538,23 +1667,92 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
                struct ondisk_cache_entry_extended *ondisk2;
                ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
                ondisk2->flags2 = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
-               name = ondisk2->name;
+               return ondisk2->name;
        }
-       else
-               name = ondisk->name;
-       memcpy(name, ce->name, ce_namelen(ce));
+       else {
+               return ondisk->name;
+       }
+}
+
+static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce,
+                         struct strbuf *previous_name)
+{
+       int size;
+       struct ondisk_cache_entry *ondisk;
+       char *name;
+       int result;
+
+       if (!previous_name) {
+               size = ondisk_ce_size(ce);
+               ondisk = xcalloc(1, size);
+               name = copy_cache_entry_to_ondisk(ondisk, ce);
+               memcpy(name, ce->name, ce_namelen(ce));
+       } else {
+               int common, to_remove, prefix_size;
+               unsigned char to_remove_vi[16];
+               for (common = 0;
+                    (ce->name[common] &&
+                     common < previous_name->len &&
+                     ce->name[common] == previous_name->buf[common]);
+                    common++)
+                       ; /* still matching */
+               to_remove = previous_name->len - common;
+               prefix_size = encode_varint(to_remove, to_remove_vi);
+
+               if (ce->ce_flags & CE_EXTENDED)
+                       size = offsetof(struct ondisk_cache_entry_extended, name);
+               else
+                       size = offsetof(struct ondisk_cache_entry, name);
+               size += prefix_size + (ce_namelen(ce) - common + 1);
+
+               ondisk = xcalloc(1, size);
+               name = copy_cache_entry_to_ondisk(ondisk, ce);
+               memcpy(name, to_remove_vi, prefix_size);
+               memcpy(name + prefix_size, ce->name + common, ce_namelen(ce) - common);
+
+               strbuf_splice(previous_name, common, to_remove,
+                             ce->name + common, ce_namelen(ce) - common);
+       }
+
+       result = ce_write(c, fd, ondisk, size);
+       free(ondisk);
+       return result;
+}
+
+static int has_racy_timestamp(struct index_state *istate)
+{
+       int entries = istate->cache_nr;
+       int i;
 
-       return ce_write(c, fd, ondisk, size);
+       for (i = 0; i < entries; i++) {
+               struct cache_entry *ce = istate->cache[i];
+               if (is_racy_timestamp(istate, ce))
+                       return 1;
+       }
+       return 0;
+}
+
+/*
+ * Opportunisticly update the index but do not complain if we can't
+ */
+void update_index_if_able(struct index_state *istate, struct lock_file *lockfile)
+{
+       if ((istate->cache_changed || has_racy_timestamp(istate)) &&
+           !write_index(istate, lockfile->fd))
+               commit_locked_index(lockfile);
+       else
+               rollback_lock_file(lockfile);
 }
 
 int write_index(struct index_state *istate, int newfd)
 {
        git_SHA_CTX c;
        struct cache_header hdr;
-       int i, err, removed, extended;
+       int i, err, removed, extended, hdr_version;
        struct cache_entry **cache = istate->cache;
        int entries = istate->cache_nr;
        struct stat st;
+       struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
 
        for (i = removed = extended = 0; i < entries; i++) {
                if (cache[i]->ce_flags & CE_REMOVE)
@@ -1568,24 +1766,34 @@ int write_index(struct index_state *istate, int newfd)
                }
        }
 
+       if (!istate->version)
+               istate->version = INDEX_FORMAT_DEFAULT;
+
+       /* demote version 3 to version 2 when the latter suffices */
+       if (istate->version == 3 || istate->version == 2)
+               istate->version = extended ? 3 : 2;
+
+       hdr_version = istate->version;
+
        hdr.hdr_signature = htonl(CACHE_SIGNATURE);
-       /* for extended format, increase version so older git won't try to read it */
-       hdr.hdr_version = htonl(extended ? 3 : 2);
+       hdr.hdr_version = htonl(hdr_version);
        hdr.hdr_entries = htonl(entries - removed);
 
        git_SHA1_Init(&c);
        if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
                return -1;
 
+       previous_name = (hdr_version == 4) ? &previous_name_buf : NULL;
        for (i = 0; i < entries; i++) {
                struct cache_entry *ce = cache[i];
                if (ce->ce_flags & CE_REMOVE)
                        continue;
                if (!ce_uptodate(ce) && is_racy_timestamp(istate, ce))
                        ce_smudge_racily_clean_entry(ce);
-               if (ce_write_entry(&c, newfd, ce) < 0)
+               if (ce_write_entry(&c, newfd, ce, previous_name) < 0)
                        return -1;
        }
+       strbuf_release(&previous_name_buf);
 
        /* Write extension data here */
        if (istate->cache_tree) {