@matheusbsbs / matheus-bagliano / commits / 5723fe7e3c

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Avoid cross-directory renames and linking on object creation

Instead of creating new temporary objects in the top-level git object directory, create them in the same directory they will finally end up in anyway. This avoids making the final atomic "rename to stable name" operation be a cross-directory event, which makes it a lot easier for various filesystems. Several filesystems do things like change the inode number when moving files across directories (or refuse to do it entirely). In particular, it can also cause problems for NFS implementations that change the filehandle of a file when it moves to a different directory, like the old user-space NFS server did, and like the Linux knfsd still does if you don't export your filesystems with 'no_subtree_check' or if you export a filesystem that doesn't have stable inode numbers across renames). This change also obviously implies creating the object fan-out subdirectory at tempfile creation time, rather than at the final move_temp_to_file() time. Which actually accounts for most of the size of the patch. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Linus Torvalds committed Jun 14, 2008 at 10:50 UTC 5723fe7e3cbbefae78bfb79c46b7716eef76fe52

1 file changed +42 -41

sha1_file.c

+42 -41

@@ -2018,49 +2018,12 @@ static void write_sha1_file_prepare(const void *buf, unsigned long len,

2018 SHA1_Final(sha1, &c);

2019 }

2020

2021 -/*

2022 - * Link the tempfile to the final place, possibly creating the

2023 - * last directory level as you do so.

2024 - *

2025 - * Returns the errno on failure, 0 on success.

2026 - */

2027 -static int link_temp_to_file(const char *tmpfile, const char *filename)

2028 -{

2029 - int ret;

2030 - char *dir;

2031 -

2032 - if (!link(tmpfile, filename))

2033 - return 0;

2034 -

2035 - /*

2036 - * Try to mkdir the last path component if that failed.

2037 - *

2038 - * Re-try the "link()" regardless of whether the mkdir

2039 - * succeeds, since a race might mean that somebody

2040 - * else succeeded.

2041 - */

2042 - ret = errno;

2043 - dir = strrchr(filename, '/');

2044 - if (dir) {

2045 - *dir = 0;

2046 - if (!mkdir(filename, 0777) && adjust_shared_perm(filename)) {

2047 - *dir = '/';

2048 - return -2;

2049 - }

2050 - *dir = '/';

2051 - if (!link(tmpfile, filename))

2052 - return 0;

2053 - ret = errno;

2054 - }

2055 - return ret;

2056 -}

2057 -

2021 /*

2022 * Move the just written object into its final resting place

2023 */

2024 int move_temp_to_file(const char *tmpfile, const char *filename)

2025 {

2063 - int ret = link_temp_to_file(tmpfile, filename);

2026 + int ret = link(tmpfile, filename);

2027

2028 /*

2029 * Coda hack - coda doesn't like cross-directory links,

@@ -2114,6 +2077,46 @@ static void close_sha1_file(int fd)

2077 die("unable to write sha1 file");

2078 }

2079

2080 +/* Size of directory component, including the ending '/' */

2081 +static inline int directory_size(const char *filename)

2082 +{

2083 + const char *s = strrchr(filename, '/');

2084 + if (!s)

2085 + return 0;

2086 + return s - filename + 1;

2087 +}

2088 +

2089 +/*

2090 + * This creates a temporary file in the same directory as the final

2091 + * 'filename'

2092 + *

2093 + * We want to avoid cross-directory filename renames, because those

2094 + * can have problems on various filesystems (FAT, NFS, Coda).

2095 + */

2096 +static int create_tmpfile(char *buffer, size_t bufsiz, const char *filename)

2097 +{

2098 + int fd, dirlen = directory_size(filename);

2099 +

2100 + if (dirlen + 20 > bufsiz) {

2101 + errno = ENAMETOOLONG;

2102 + return -1;

2103 + }

2104 + memcpy(buffer, filename, dirlen);

2105 + strcpy(buffer + dirlen, "tmp_obj_XXXXXX");

2106 + fd = mkstemp(buffer);

2107 + if (fd < 0 && dirlen) {

2108 + /* Make sure the directory exists */

2109 + buffer[dirlen-1] = 0;

2110 + if (mkdir(buffer, 0777) && adjust_shared_perm(buffer))

2111 + return -1;

2112 +

2113 + /* Try again */

2114 + strcpy(buffer + dirlen - 1, "/tmp_obj_XXXXXX");

2115 + fd = mkstemp(buffer);

2116 + }

2117 + return fd;

2118 +}

2119 +

2120 static int write_loose_object(const unsigned char *sha1, char *hdr, int hdrlen,

2121 void *buf, unsigned long len, time_t mtime)

2122 {

@@ -2138,9 +2141,7 @@ static int write_loose_object(const unsigned char *sha1, char *hdr, int hdrlen,

2141 return error("sha1 file %s: %s\n", filename, strerror(errno));

2142 }

2143

2141 - snprintf(tmpfile, sizeof(tmpfile), "%s/tmp_obj_XXXXXX", get_object_directory());

2142 -

2143 - fd = mkstemp(tmpfile);

2144 + fd = create_tmpfile(tmpfile, sizeof(tmpfile), filename);

2145 if (fd < 0) {

2146 if (errno == EPERM)

2147 return error("insufficient permission for adding an object to repository database %s\n", get_object_directory());