From 678eb55f5da174fce21f686f0073d56904c081c9 Mon Sep 17 00:00:00 2001 From: "brian m. carlson" Date: Thu, 12 Oct 2023 16:09:29 +0000 Subject: [PATCH 1/2] t: add a test helper to truncate files In a future commit, we're going to work with some large files which will be at least 4 GiB in size. To take advantage of the sparseness functionality on most Unix systems and avoid running the system out of disk, it would be convenient to use truncate(2) to simply create a sparse file of sufficient size. However, the GNU truncate(1) utility isn't portable, so let's write a tiny test helper that does the work for us. Signed-off-by: brian m. carlson Signed-off-by: Junio C Hamano --- Makefile | 1 + t/helper/test-tool.c | 1 + t/helper/test-tool.h | 1 + t/helper/test-truncate.c | 25 +++++++++++++++++++++++++ 4 files changed, 28 insertions(+) create mode 100644 t/helper/test-truncate.c diff --git a/Makefile b/Makefile index 5776309365357a..3a6889d2bc8282 100644 --- a/Makefile +++ b/Makefile @@ -852,6 +852,7 @@ TEST_BUILTINS_OBJS += test-submodule-nested-repo-config.o TEST_BUILTINS_OBJS += test-submodule.o TEST_BUILTINS_OBJS += test-subprocess.o TEST_BUILTINS_OBJS += test-trace2.o +TEST_BUILTINS_OBJS += test-truncate.o TEST_BUILTINS_OBJS += test-urlmatch-normalization.o TEST_BUILTINS_OBJS += test-userdiff.o TEST_BUILTINS_OBJS += test-wildmatch.o diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c index abe8a785eb6510..9bd223b36514d8 100644 --- a/t/helper/test-tool.c +++ b/t/helper/test-tool.c @@ -86,6 +86,7 @@ static struct test_cmd cmds[] = { { "submodule-nested-repo-config", cmd__submodule_nested_repo_config }, { "subprocess", cmd__subprocess }, { "trace2", cmd__trace2 }, + { "truncate", cmd__truncate }, { "userdiff", cmd__userdiff }, { "urlmatch-normalization", cmd__urlmatch_normalization }, { "xml-encode", cmd__xml_encode }, diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h index ea2672436c9ab5..f41a4d0aa86990 100644 --- a/t/helper/test-tool.h +++ b/t/helper/test-tool.h @@ -79,6 +79,7 @@ int cmd__submodule_config(int argc, const char **argv); int cmd__submodule_nested_repo_config(int argc, const char **argv); int cmd__subprocess(int argc, const char **argv); int cmd__trace2(int argc, const char **argv); +int cmd__truncate(int argc, const char **argv); int cmd__userdiff(int argc, const char **argv); int cmd__urlmatch_normalization(int argc, const char **argv); int cmd__xml_encode(int argc, const char **argv); diff --git a/t/helper/test-truncate.c b/t/helper/test-truncate.c new file mode 100644 index 00000000000000..3931deaec7dcda --- /dev/null +++ b/t/helper/test-truncate.c @@ -0,0 +1,25 @@ +#include "test-tool.h" +#include "git-compat-util.h" + +/* + * Truncate a file to the given size. + */ +int cmd__truncate(int argc, const char **argv) +{ + char *p = NULL; + uintmax_t sz = 0; + int fd = -1; + + if (argc != 3) + die("expected filename and size"); + + sz = strtoumax(argv[2], &p, 0); + if (*p) + die("invalid size"); + + fd = xopen(argv[1], O_WRONLY | O_CREAT, 0600); + + if (ftruncate(fd, (off_t) sz) < 0) + die_errno("failed to truncate file"); + return 0; +} From 5143ac07b17e2b025865378fce24cc11ac7bf8b1 Mon Sep 17 00:00:00 2001 From: Jason Hatton Date: Thu, 12 Oct 2023 16:09:30 +0000 Subject: [PATCH 2/2] Prevent git from rehashing 4GiB files The index stores file sizes using a uint32_t. This causes any file that is a multiple of 2^32 to have a cached file size of zero. Zero is a special value used by racily clean. This causes git to rehash every file that is a multiple of 2^32 every time git status or git commit is run. This patch mitigates the problem by making all files that are a multiple of 2^32 appear to have a size of 1<<31 instead of zero. The value of 1<<31 is chosen to keep it as far away from zero as possible to help prevent things getting mixed up with unpatched versions of git. An example would be to have a 2^32 sized file in the index of patched git. Patched git would save the file as 2^31 in the cache. An unpatched git would very much see the file has changed in size and force it to rehash the file, which is safe. The file would have to grow or shrink by exactly 2^31 and retain all of its ctime, mtime, and other attributes for old git to not notice the change. This patch does not change the behavior of any file that is not an exact multiple of 2^32. Signed-off-by: Jason D. Hatton Signed-off-by: brian m. carlson Signed-off-by: Junio C Hamano --- statinfo.c | 20 ++++++++++++++++++-- t/t7508-status.sh | 16 ++++++++++++++++ 2 files changed, 34 insertions(+), 2 deletions(-) diff --git a/statinfo.c b/statinfo.c index 17bb8966c33d6d..9367ca099cd114 100644 --- a/statinfo.c +++ b/statinfo.c @@ -2,6 +2,22 @@ #include "environment.h" #include "statinfo.h" +/* + * Munge st_size into an unsigned int. + */ +static unsigned int munge_st_size(off_t st_size) { + unsigned int sd_size = st_size; + + /* + * If the file is an exact multiple of 4 GiB, modify the value so it + * doesn't get marked as racily clean (zero). + */ + if (!sd_size && st_size) + return 0x80000000; + else + return sd_size; +} + void fill_stat_data(struct stat_data *sd, struct stat *st) { sd->sd_ctime.sec = (unsigned int)st->st_ctime; @@ -12,7 +28,7 @@ void fill_stat_data(struct stat_data *sd, struct stat *st) sd->sd_ino = st->st_ino; sd->sd_uid = st->st_uid; sd->sd_gid = st->st_gid; - sd->sd_size = st->st_size; + sd->sd_size = munge_st_size(st->st_size); } int match_stat_data(const struct stat_data *sd, struct stat *st) @@ -51,7 +67,7 @@ int match_stat_data(const struct stat_data *sd, struct stat *st) changed |= INODE_CHANGED; #endif - if (sd->sd_size != (unsigned int) st->st_size) + if (sd->sd_size != munge_st_size(st->st_size)) changed |= DATA_CHANGED; return changed; diff --git a/t/t7508-status.sh b/t/t7508-status.sh index 6928fd89f5d887..6c46648e1128cc 100755 --- a/t/t7508-status.sh +++ b/t/t7508-status.sh @@ -1745,4 +1745,20 @@ test_expect_success 'slow status advice when core.untrackedCache true, and fsmon ) ' +test_expect_success EXPENSIVE 'status does not re-read unchanged 4 or 8 GiB file' ' + ( + mkdir large-file && + cd large-file && + # Files are 2 GiB, 4 GiB, and 8 GiB sparse files. + test-tool truncate file-a 0x080000000 && + test-tool truncate file-b 0x100000000 && + test-tool truncate file-c 0x200000000 && + # This will be slow. + git add file-a file-b file-c && + git commit -m "add large files" && + git diff-index HEAD file-a file-b file-c >actual && + test_must_be_empty actual + ) +' + test_done