From 23e93ca6674f0d9da6834bbc2eba6cc3cd9ba6ff Mon Sep 17 00:00:00 2001 From: Matteo Croce Date: Mon, 30 Sep 2024 01:43:11 +0200 Subject: [PATCH 1/4] reflink: align data on block size on archive create Add a --reflink option which, on archive creation, aligns file data on a 4k block boundary. This is done by padding the extended header with a standard "comment" pax record, which is ignored on extraction. For this reason the option implies --format=posix. This will be used when extracting files using reflinks, as one of the requirements is that the data is aligned on a 4k boundary. The alignment is skipped, with a warning, in the cases where it cannot work: a non-posix format selected explicitly, compressed, multi-volume or remote archives, appending to an existing archive, sparse members (which cannot be cloned on extraction), and --pax-option keyword overrides, which would invalidate the computed padding. * src/tar.c (options, parse_opt): New option --reflink. (decode_options): Warn about combinations that defeat the alignment: an explicit non-posix format, compressed, multi-volume or remote archives, appending to an existing archive. * src/common.h (reflink_option): New global. (REFLINK_BLOCK_SIZE): New constant. (round_up): New inline function. (struct xheader_comment): New type. (xheader_comment_overridden_p): New prototype. * src/create.c (start_header): Pad the extended header with a "comment" record sized so that the member data starts on a REFLINK_BLOCK_SIZE boundary. * src/xheader.c (comment_coder): New coder. (xheader_comment_overridden_p): New function. (xhdr_tab): Use comment_coder for the "comment" keyword. --- src/common.h | 26 ++++++++++++++++++++++++++ src/create.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ src/tar.c | 34 ++++++++++++++++++++++++++++++++++ src/xheader.c | 23 ++++++++++++++++++++++- 4 files changed, 129 insertions(+), 1 deletion(-) diff --git a/src/common.h b/src/common.h index e835d888..9326a360 100644 --- a/src/common.h +++ b/src/common.h @@ -276,6 +276,9 @@ extern int acls_option; /* If true, save the user and root xattrs. */ extern bool xattrs_option; +/* If true, use reflinks when possible. */ +extern bool reflink_option; + /* When set, strip the given number of file name components from the file name before extracting */ extern idx_t strip_name_components; @@ -395,6 +398,20 @@ extern bool show_transformed_names_option; timestamps from archives with an unusual member order. It is automatically set for incremental archives. */ extern bool delay_directory_restore_option; + +/* The block size that --reflink aligns member data to; FICLONERANGE + requires source and destination ranges aligned to the filesystem + block size, for which this is a safe upper bound. */ +enum { REFLINK_BLOCK_SIZE = 4096 }; + +/* Rounds up n to the next multiple of m. Only works if m is a power of two. */ +COMMON_INLINE off_t +round_up (off_t n, off_t m) +{ + m--; + return (n + m) & ~m; +} + /* Declarations for each module. */ @@ -927,6 +944,14 @@ void update_archive (void); /* Module xheader.c. */ +/* Value for xheader_store of a "comment" keyword; used by --reflink + to pad the extended header to a REFLINK_BLOCK_SIZE boundary. */ +struct xheader_comment +{ + char const *comment; + idx_t length; +}; + void xheader_decode (struct tar_stat_info *stat); void xheader_decode_global (struct xheader *xhdr); void xheader_store (char const *keyword, struct tar_stat_info *st, @@ -944,6 +969,7 @@ void xheader_string_begin (struct xheader *xhdr); void xheader_string_add (struct xheader *xhdr, char const *s); bool xheader_string_end (struct xheader *xhdr, char const *keyword); bool xheader_keyword_deleted_p (const char *kw); +bool xheader_comment_overridden_p (void); char *xheader_format_name (struct tar_stat_info *st, const char *fmt, intmax_t n); void xheader_xattr_init (struct tar_stat_info *st); diff --git a/src/create.c b/src/create.c index bf9f9838..fcdca371 100644 --- a/src/create.c +++ b/src/create.c @@ -944,6 +944,53 @@ start_header (struct tar_stat_info *st) if (xattrs_option) for (idx_t i = 0; i < st->xattr_map.xm_size; i++) xheader_store (st->xattr_map.xm_map[i].xkey, st, &i); + if (reflink_option && S_ISREG (st->stat.st_mode) && st->stat.st_size + /* Sparse members add GNU.sparse.* records after this point, + which would invalidate the alignment; they cannot be + reflinked on extraction anyway. */ + && ! (sparse_option && ST_IS_SPARSE (st->stat))) + { + if (xheader_comment_overridden_p ()) + { + static bool warned; + if (!warned) + { + paxwarn (0, _("--pax-option keyword overrides prevent" + " --reflink data alignment")); + warned = true; + } + } + else + { + /* On disk the member is laid out as the pax extended header + block, the pax data (rounded up to BLOCKSIZE), the ustar + header block, then the file data. Choose the comment + payload length so that the file data lands on a + REFLINK_BLOCK_SIZE boundary. COMMENT_OVERHEAD is the + record's own framing (up to 4 length digits + " comment=" + + "\n"); an over-estimate is harmless because the + BLOCKSIZE rounding of the pax data absorbs the few unused + bytes. */ + enum { COMMENT_OVERHEAD = 14 }; + off_t pos = (records_written * record_size + + (current_block->buffer - record_start->buffer)); + off_t before = (pos + 2 * BLOCKSIZE + st->xhdr.size + + COMMENT_OVERHEAD); + off_t n = round_up (before, REFLINK_BLOCK_SIZE) - before; + static char comment_buf[REFLINK_BLOCK_SIZE]; + + if (comment_buf[0] == 0) + memset (comment_buf, ' ', sizeof (comment_buf)); + + struct xheader_comment comment = + { + .comment = comment_buf, + .length = n, + }; + + xheader_store ("comment", st, &comment); + } + } } return header; diff --git a/src/tar.c b/src/tar.c index a920d9c2..4b104158 100644 --- a/src/tar.c +++ b/src/tar.c @@ -89,6 +89,7 @@ bool xattrs_option; idx_t strip_name_components; bool show_omitted_dirs_option; bool sparse_option; +bool reflink_option; intmax_t tar_sparse_major; intmax_t tar_sparse_minor; enum hole_detection_method hole_detection; @@ -406,6 +407,7 @@ enum QUOTING_STYLE_OPTION, RECORD_SIZE_OPTION, RECURSIVE_UNLINK_OPTION, + REFLINK_OPTION, REMOVE_FILES_OPTION, RESTRICT_OPTION, RMT_COMMAND_OPTION, @@ -587,6 +589,9 @@ static struct argp_option options[] = { {"check-device", CHECK_DEVICE_OPTION, NULL, 0, N_("check device numbers when creating incremental archives (default)"), GRID_MODIFIER }, + {"reflink", REFLINK_OPTION, NULL, 0, + N_("align file data when creating an archive, clone file data when" + " extracting"), GRID_MODIFIER }, {NULL, 0, NULL, 0, N_("Overwrite control:"), GRH_OVERWRITE }, @@ -1763,6 +1768,11 @@ parse_opt (int key, char *arg, struct argp_state *state) sparse_option = true; break; + case REFLINK_OPTION: + set_archive_format ("posix"); + reflink_option = true; + break; + case SKIP_OLD_FILES_OPTION: set_old_files_option (SKIP_OLD_FILES, args->loc); break; @@ -2502,6 +2512,30 @@ decode_options (int argc, char **argv) | format_mask (GNU_FORMAT) | format_mask (POSIX_FORMAT)); + /* Data alignment for --reflink needs the pax comment record and a + final archive that is a plain uncompressed local file; warn about + combinations that silently defeat it. */ + if (reflink_option) + { + if (subcommand_option == CREATE_SUBCOMMAND) + { + if (archive_format != POSIX_FORMAT) + paxwarn (0, _("--reflink data alignment requires the posix" + " format")); + if (multi_volume_option) + paxwarn (0, _("--reflink is ineffective with multi-volume" + " archives")); + if (use_compress_program_option) + paxwarn (0, _("--reflink is ineffective with compressed" + " archives")); + } + else if (subcommand_option == APPEND_SUBCOMMAND + || subcommand_option == UPDATE_SUBCOMMAND + || subcommand_option == CAT_SUBCOMMAND) + paxwarn (0, _("--reflink is ineffective when appending to an" + " archive")); + } + if (occurrence_option) { if (!name_more_files ()) diff --git a/src/xheader.c b/src/xheader.c index 05f905ed..8df4098b 100644 --- a/src/xheader.c +++ b/src/xheader.c @@ -129,6 +129,17 @@ xheader_keyword_override_p (const char *keyword) return false; } +/* Return true if pax keyword overrides prevent sizing the "comment" + record used by --reflink to align member data: 'keyword:=value' + overrides are appended after the comment record is sized, and a + deleted "comment" keyword drops the record altogether. */ +bool +xheader_comment_overridden_p (void) +{ + return keyword_override_list != NULL + || xheader_keyword_deleted_p ("comment"); +} + static void xheader_list_append (struct keyword_list **root, char const *kw, char const *value) @@ -1662,9 +1673,19 @@ sparse_minor_decoder (struct tar_stat_info *st, st->sparse_minor = u; } +static void +comment_coder (struct tar_stat_info const *UNNAMED (st), + char const *keyword, + struct xheader *xhdr, + void const *data) +{ + struct xheader_comment const *comment = data; + xheader_print_n (xhdr, keyword, comment->comment, comment->length); +} + struct xhdr_tab const xhdr_tab[] = { { "atime", atime_coder, atime_decoder, 0, false }, - { "comment", dummy_coder, dummy_decoder, 0, false }, + { "comment", comment_coder, dummy_decoder, 0, false }, { "charset", dummy_coder, dummy_decoder, 0, false }, { "ctime", ctime_coder, ctime_decoder, 0, false }, { "gid", gid_coder, gid_decoder, 0, false }, -- 2.50.1