Add core.symlinks to mark filesystems that do not support symbolic links.

Some file systems that can host git repositories and their working copies
do not support symbolic links. But then if the repository contains a symbolic
link, it is impossible to check out the working copy.

This patch enables partial support of symbolic links so that it is possible
to check out a working copy on such a file system.  A new flag
core.symlinks (which is true by default) can be set to false to indicate
that the filesystem does not support symbolic links. In this case, symbolic
links that exist in the trees are checked out as small plain files, and
checking in modifications of these files preserve the symlink property in
the database (as long as an entry exists in the index).

Of course, this does not magically make symbolic links work on such defective
file systems; hence, this solution does not help if the working copy relies
on that an entry is a real symbolic link.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <junkio@cox.net>

12 files changed, 101 insertions, 12 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d2b4a05..b809772 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -117,6 +117,13 @@ core.fileMode::
 	the working copy are ignored; useful on broken filesystems like FAT.
 	See gitlink:git-update-index[1]. True by default.
 
+core.symlinks::
+	If false, symbolic links are checked out as small plain files that
+	contain the link text. gitlink:git-update-index[1] and
+	gitlink:git-add[1] will not change the recorded type to regular
+	file. Useful on filesystems like FAT that do not support
+	symbolic links. True by default.
+
 core.gitProxy::
 	A "proxy command" to execute (as 'command host port') instead
 	of establishing direct connection to the remote server when
diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index b161c8b..cd5e014 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -295,6 +295,11 @@ in the index and the file mode on the filesystem if they differ only on
 executable bit.   On such an unfortunate filesystem, you may
 need to use `git-update-index --chmod=`.
 
+Quite similarly, if `core.symlinks` configuration variable is set
+to 'false' (see gitlink:git-config[1]), symbolic links are checked out
+as plain files, and this command does not modify a recorded file mode
+from symbolic link to regular file.
+
 The command looks at `core.ignorestat` configuration variable.  See
 'Using "assume unchanged" bit' section above.
 
diff --git a/builtin-apply.c b/builtin-apply.c
index 38f6475..5393510 100644
--- a/builtin-apply.c
+++ b/builtin-apply.c
@@ -2359,7 +2359,7 @@ static int try_create_file(const char *path, unsigned int mode, const char *buf,
 	char *nbuf;
 	unsigned long nsize;
 
-	if (S_ISLNK(mode))
+	if (has_symlinks && S_ISLNK(mode))
 		/* Although buf:size is counted string, it also is NUL
 		 * terminated.
 		 */
diff --git a/builtin-update-index.c b/builtin-update-index.c
index 65246da..71cef63 100644
--- a/builtin-update-index.c
+++ b/builtin-update-index.c
@@ -109,11 +109,11 @@ static int add_file_to_cache(const char *path)
 	ce->ce_flags = htons(namelen);
 	fill_stat_cache_info(ce, &st);
 
-	if (trust_executable_bit)
+	if (trust_executable_bit && has_symlinks)
 		ce->ce_mode = create_ce_mode(st.st_mode);
 	else {
-		/* If there is an existing entry, pick the mode bits
-		 * from it, otherwise assume unexecutable.
+		/* If there is an existing entry, pick the mode bits and type
+		 * from it, otherwise assume unexecutable regular file.
 		 */
 		struct cache_entry *ent;
 		int pos = cache_name_pos(path, namelen);
diff --git a/cache.h b/cache.h
index 8018b2c..c291163 100644
--- a/cache.h
+++ b/cache.h
@@ -108,7 +108,10 @@ static inline unsigned int create_ce_mode(unsigned int mode)
 }
 static inline unsigned int ce_mode_from_stat(struct cache_entry *ce, unsigned int mode)
 {
-	extern int trust_executable_bit;
+	extern int trust_executable_bit, has_symlinks;
+	if (!has_symlinks && S_ISREG(mode) &&
+	    ce && S_ISLNK(ntohl(ce->ce_mode)))
+		return ce->ce_mode;
 	if (!trust_executable_bit && S_ISREG(mode)) {
 		if (ce && S_ISREG(ntohl(ce->ce_mode)))
 			return ce->ce_mode;
@@ -215,6 +218,7 @@ extern int delete_ref(const char *, unsigned char *sha1);
 /* Environment bits from configuration mechanism */
 extern int use_legacy_headers;
 extern int trust_executable_bit;
+extern int has_symlinks;
 extern int assume_unchanged;
 extern int prefer_symlink_refs;
 extern int log_all_ref_updates;
diff --git a/config.c b/config.c
index 0ff413b..7ac3947 100644
--- a/config.c
+++ b/config.c
@@ -269,6 +269,11 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.symlinks")) {
+		has_symlinks = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.bare")) {
 		is_bare_repository_cfg = git_config_bool(var, value);
 		return 0;
diff --git a/diff-lib.c b/diff-lib.c
index 2e91619..f70888f 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -346,6 +346,9 @@ int run_diff_files(struct rev_info *revs, int silent_on_removed)
 		    S_ISREG(newmode) && S_ISREG(oldmode) &&
 		    ((newmode ^ oldmode) == 0111))
 			newmode = oldmode;
+		else if (!has_symlinks &&
+		    S_ISREG(newmode) && S_ISLNK(oldmode))
+			newmode = oldmode;
 		diff_change(&revs->diffopt, oldmode, newmode,
 			    ce->sha1, (changed ? null_sha1 : ce->sha1),
 			    ce->name, NULL);
diff --git a/entry.c b/entry.c
index 21b5f2e..d72f811 100644
--- a/entry.c
+++ b/entry.c
@@ -111,9 +111,12 @@ static int write_entry(struct cache_entry *ce, char *path, struct checkout *stat
 			return error("git-checkout-index: unable to write file %s", path);
 		break;
 	case S_IFLNK:
-		if (to_tempfile) {
-			strcpy(path, ".merge_link_XXXXXX");
-			fd = mkstemp(path);
+		if (to_tempfile || !has_symlinks) {
+			if (to_tempfile) {
+				strcpy(path, ".merge_link_XXXXXX");
+				fd = mkstemp(path);
+			} else
+				fd = create_file(path, 0666);
 			if (fd < 0) {
 				free(new);
 				return error("git-checkout-index: unable to create "
diff --git a/environment.c b/environment.c
index 570e32a..49486dd 100644
--- a/environment.c
+++ b/environment.c
@@ -13,6 +13,7 @@ char git_default_email[MAX_GITNAME];
 char git_default_name[MAX_GITNAME];
 int use_legacy_headers = 1;
 int trust_executable_bit = 1;
+int has_symlinks = 1;
 int assume_unchanged;
 int prefer_symlink_refs;
 int is_bare_repository_cfg = -1; /* unspecified */
diff --git a/read-cache.c b/read-cache.c
index 7a104e3..4a972b4 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -125,7 +125,9 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
 			changed |= MODE_CHANGED;
 		break;
 	case S_IFLNK:
-		changed |= !S_ISLNK(st->st_mode) ? TYPE_CHANGED : 0;
+		if (!S_ISLNK(st->st_mode) &&
+		    (has_symlinks || !S_ISREG(st->st_mode)))
+			changed |= TYPE_CHANGED;
 		break;
 	default:
 		die("internal error: ce_mode is %o", ntohl(ce->ce_mode));
@@ -344,11 +346,11 @@ int add_file_to_index(const char *path, int verbose)
 	ce->ce_flags = htons(namelen);
 	fill_stat_cache_info(ce, &st);
 
-	if (trust_executable_bit)
+	if (trust_executable_bit && has_symlinks)
 		ce->ce_mode = create_ce_mode(st.st_mode);
 	else {
-		/* If there is an existing entry, pick the mode bits
-		 * from it, otherwise assume unexecutable.
+		/* If there is an existing entry, pick the mode bits and type
+		 * from it, otherwise assume unexecutable regular file.
 		 */
 		struct cache_entry *ent;
 		int pos = cache_name_pos(path, namelen);
diff --git a/t/t2005-checkout-index-symlinks.sh b/t/t2005-checkout-index-symlinks.sh
new file mode 100755
index 0000000..e34a515
--- /dev/null
+++ b/t/t2005-checkout-index-symlinks.sh
@@ -0,0 +1,28 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Johannes Sixt
+#
+
+test_description='git-checkout-index on filesystem w/o symlinks test.
+
+This tests that git-checkout-index creates a symbolic link as a plain
+file if core.symlinks is false.'
+
+. ./test-lib.sh
+
+test_expect_success \
+'preparation' '
+git-config core.symlinks false &&
+l=$(echo -n file | git-hash-object -t blob -w --stdin) &&
+echo "120000 $l	symlink" | git-update-index --index-info'
+
+test_expect_success \
+'the checked-out symlink must be a file' '
+git-checkout-index symlink &&
+test -f symlink'
+
+test_expect_success \
+'the file must be the blob we added during the setup' '
+test "$(git-hash-object -t blob symlink)" = $l'
+
+test_done
diff --git a/t/t2102-update-index-symlinks.sh b/t/t2102-update-index-symlinks.sh
new file mode 100755
index 0000000..969ef89
--- /dev/null
+++ b/t/t2102-update-index-symlinks.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Johannes Sixt
+#
+
+test_description='git-update-index on filesystem w/o symlinks test.
+
+This tests that git-update-index keeps the symbolic link property
+even if a plain file is in the working tree if core.symlinks is false.'
+
+. ./test-lib.sh
+
+test_expect_success \
+'preparation' '
+git-config core.symlinks false &&
+l=$(echo -n file | git-hash-object -t blob -w --stdin) &&
+echo "120000 $l	symlink" | git-update-index --index-info'
+
+test_expect_success \
+'modify the symbolic link' '
+echo -n new-file > symlink &&
+git-update-index symlink'
+
+test_expect_success \
+'the index entry must still be a symbolic link' '
+case "`git-ls-files --stage --cached symlink`" in
+120000" "*symlink) echo ok;;
+*) echo fail; git-ls-files --stage --cached symlink; (exit 1);;
+esac'
+
+test_done