{"id":207540,"date":"2025-07-08T08:12:32","date_gmt":"2025-07-08T00:12:32","guid":{"rendered":"https:\/\/server.hk\/cnblog\/207540\/"},"modified":"2025-07-08T08:12:32","modified_gmt":"2025-07-08T00:12:32","slug":"%e8%bf%99%e6%ae%b5%e4%bb%a3%e7%a0%81%e5%a6%82%e4%bd%95%e7%94%9f%e6%88%90%e5%86%85%e5%ad%98%e5%af%b9%e9%bd%90%e7%9a%84%e5%88%87%e7%89%87%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/207540\/","title":{"rendered":"\u8fd9\u6bb5\u4ee3\u7801\u5982\u4f55\u751f\u6210\u5185\u5b58\u5bf9\u9f50\u7684\u5207\u7247\uff1f"},"content":{"rendered":"

<\/b> <\/p>\n

\u5f53\u524d\u4f4d\u7f6e\uff1a ><\/span> ><\/span> ><\/span> ><\/span> \u8fd9\u6bb5\u4ee3\u7801\u5982\u4f55\u751f\u6210\u5185\u5b58\u5bf9\u9f50\u7684\u5207\u7247\uff1f<\/span><\/p>\n

\u6765\u6e90\uff1astackoverflow<\/span>
\n2024-04-23 14:18:36<\/span>
\n<\/i>0\u6d4f\u89c8<\/span>
\n<\/i>\u6536\u85cf<\/span> <\/p>\n

\u79ef\u7d2f\u77e5\u8bc6\uff0c\u80dc\u8fc7\u79ef\u84c4\u91d1\u94f6\uff01\u6bd5\u7adf\u5728Golang\u5f00\u53d1\u7684\u8fc7\u7a0b\u4e2d\uff0c\u4f1a\u9047\u5230\u5404\u79cd\u5404\u6837\u7684\u95ee\u9898\uff0c\u5f80\u5f80\u90fd\u662f\u4e00\u4e9b\u7ec6\u8282\u77e5\u8bc6\u70b9\u8fd8\u6ca1\u6709\u638c\u63e1\u597d\u800c\u5bfc\u81f4\u7684\uff0c\u56e0\u6b64\u57fa\u7840\u77e5\u8bc6\u70b9\u7684\u79ef\u7d2f\u662f\u5f88\u91cd\u8981\u7684\u3002\u4e0b\u9762\u672c\u6587\u300a\u8fd9\u6bb5\u4ee3\u7801\u5982\u4f55\u751f\u6210\u5185\u5b58\u5bf9\u9f50\u7684\u5207\u7247\uff1f\u300b\uff0c\u5c31\u5e26\u5927\u5bb6\u8bb2\u89e3\u4e00\u4e0b\u77e5\u8bc6\u70b9\uff0c\u82e5\u662f\u4f60\u5bf9\u672c\u6587\u611f\u5174\u8da3\uff0c\u6216\u8005\u662f\u60f3\u641e\u61c2\u5176\u4e2d\u67d0\u4e2a\u77e5\u8bc6\u70b9\uff0c\u5c31\u8bf7\u4f60\u7ee7\u7eed\u5f80\u4e0b\u770b\u5427~<\/p>\n

\u95ee\u9898\u5185\u5bb9
\n <\/p>\n

\u6211\u6b63\u5728\u5c1d\u8bd5\u5728 linux \u4e0a\u8fdb\u884c\u76f4\u63a5 i\/o\uff0c\u56e0\u6b64\u6211\u9700\u8981\u521b\u5efa\u5185\u5b58\u5bf9\u9f50\u7f13\u51b2\u533a\u3002\u6211\u590d\u5236\u4e86\u4e00\u4e9b\u4ee3\u7801\u6765\u6267\u884c\u6b64\u64cd\u4f5c\uff0c\u4f46\u6211\u4e0d\u660e\u767d\u5b83\u662f\u5982\u4f55\u5de5\u4f5c\u7684\uff1a<\/p>\n

package main\n\nimport (\n    \"fmt\"\n    \"golang.org\/x\/sys\/unix\"\n    \"unsafe\"\n    \"yottastore\/yottastore-go\/src\/yfs\/test\/utils\"\n)\n\nconst (\n    alignsize = 4096\n    blocksize = 4096\n)\n\n\/\/ looks like dark magic\nfunc alignment(block []byte, alignsize int) int {\n    return int(uintptr(unsafe.pointer(&block[0])) & uintptr(alignsize-1))\n}\n\nfunc main() {\n\n    path := \"\/path\/to\/file.txt\"\n    fd, err := unix.open(path, unix.o_rdonly|unix.o_direct, 0666)\n    defer unix.close(fd)\n\n    if err != nil {\n        panic(err)\n    }\n\n    file := make([]byte, 4096*2)\n\n    a := alignment(file, alignsize)\n\n    offset := 0\n    if a != 0 {\n        offset = alignsize - a\n    }\n\n    file = file[offset : offset+blocksize]\n\n\n    n, readerr := unix.pread(fd, file, 0)\n    \n    if readerr != nil {\n        panic(readerr)\n    }\n\n    fmt.println(a, offset, offset+utils.blocksize, len(file))\n    fmt.println(\"content is: \", string(file))\n}<\/pre>\n
\u6211\u77e5\u9053\u6211\u751f\u6210\u7684\u5207\u7247\u662f\u6211\u9700\u8981\u7684\u4e24\u500d\u5927\uff0c\u7136\u540e\u4ece\u4e2d\u63d0\u53d6\u5185\u5b58\u5bf9\u9f50\u5757\uff0c\u4f46 alignment<\/code> \u51fd\u6570\u5bf9\u6211\u6765\u8bf4\u6ca1\u6709\u610f\u4e49\u3002<\/p>\n
    \n
  • alignment<\/code> \u51fd\u6570\u5982\u4f55\u5de5\u4f5c\uff1f<\/li>\n
  • \u5982\u679c\u6211\u5c1d\u8bd5 fmt.println<\/code> \u8be5\u51fd\u6570\u7684\u4e2d\u95f4\u6b65\u9aa4\uff0c\u6211\u4f1a\u5f97\u5230\u4e0d\u540c\u7684\u7ed3\u679c\uff0c\u4e3a\u4ec0\u4e48\uff1f\u6211\u731c\u662f\u56e0\u4e3a\u89c2\u5bdf\u5b83\u4f1a\u6539\u53d8\u5b83\u7684\u5185\u5b58\u5bf9\u9f50\u65b9\u5f0f\uff08\u5c31\u50cf\u5728\u91cf\u5b50\u7269\u7406\u5b66\u4e2d\u4e00\u6837\uff1ad\uff09<\/li>\n<\/ul>\n
    \u7f16\u8f91<\/strong>\uff1a \u4ee5 fmt.println<\/code> \u4e3a\u4f8b\uff0c\u6211\u4e0d\u9700\u8981\u4efb\u4f55\u66f4\u591a\u7684\u5bf9\u9f50\uff1a<\/p>\n
    package main\nimport (\n    \"fmt\"\n    \"golang.org\/x\/sys\/unix\"\n    \"unsafe\"\n)\n\nfunc main() {\n\n    path := \"\/path\/to\/file.txt\"\n    fd, err := unix.Open(path, unix.O_RDONLY|unix.O_DIRECT, 0666)\n    defer unix.Close(fd)\n\n    if err != nil {\n        panic(err)\n    }\n\n    file := make([]byte, 4096)\n\n    fmt.Println(\"Pointer: \", &file[0])\n\n    n, readErr := unix.Pread(fd, file, 0)\n\n    fmt.Println(\"Return is: \", n)\n\n    if readErr != nil {\n        panic(readErr)\n    }\n\n    fmt.Println(\"Content is: \", string(file))\n}<\/pre>\n
     <\/p>\n
    \u6b63\u786e\u7b54\u6848<\/h2>\n
     <\/p>\n
    \u60a8\u7684 alignsize<\/code> \u7684\u503c\u4e3a 2 \u7684\u5e42\u3002\u5728\u4e8c\u8fdb\u5236\u8868\u793a\u5f62\u5f0f\u4e2d\uff0c\u5b83\u5305\u542b\u4e00\u4e2a 1<\/code> \u4f4d\uff0c\u540e\u8ddf\u5168\u96f6\uff1a<\/p>\n
    fmt.printf(\"%b\", alignsize) \/\/ 1000000000000<\/pre>\n
    \u7531 make()<\/code> \u5206\u914d\u7684\u5207\u7247\u53ef\u80fd\u5177\u6709\u6216\u591a\u6216\u5c11\u968f\u673a\u7684\u5185\u5b58\u5730\u5740\uff0c\u7531\u4e8c\u8fdb\u5236\u4e2d\u968f\u673a\u8ddf\u968f\u7684 1 \u548c 0 \u7ec4\u6210\uff1b\u6216\u8005\u66f4\u51c6\u786e\u5730\u8bf4\u662f\u5176\u540e\u5907\u6570\u7ec4\u7684\u8d77\u59cb\u5730\u5740\u3002<\/p>\n
    \u7531\u4e8e\u60a8\u5206\u914d\u4e86\u6240\u9700\u5927\u5c0f\u7684\u4e24\u500d\uff0c\u56e0\u6b64\u53ef\u4ee5\u4fdd\u8bc1\u540e\u5907\u6570\u7ec4\u5c06\u8986\u76d6\u4e00\u4e2a\u5730\u5740\u7a7a\u95f4\uff0c\u8be5\u5730\u5740\u7a7a\u95f4\u7684\u4e2d\u95f4\u67d0\u4e2a\u4f4d\u7f6e\u4ee5\u4e0e alignsize<\/code> \u7684\u4e8c\u8fdb\u5236\u8868\u793a\u5f62\u5f0f\u4e00\u6837\u591a\u7684\u96f6\u7ed3\u5c3e\uff0c\u5e76\u4e14\u5728\u6570\u7ec4\u4e2d\u5177\u6709 blocksize<\/code> \u7a7a\u95f4\u4ece\u6b64\u5f00\u59cb\u3002\u6211\u4eec\u60f3\u8981\u627e\u5230\u8fd9\u4e2a\u5730\u5740\u3002<\/p>\n
    \u8fd9\u5c31\u662f alignment()<\/code> \u51fd\u6570\u7684\u4f5c\u7528\u3002\u5b83\u4f7f\u7528 &block[0]<\/code> \u83b7\u53d6\u540e\u5907\u6570\u7ec4\u7684\u8d77\u59cb\u5730\u5740\u3002 go \u4e2d\u6ca1\u6709\u6307\u9488\u7b97\u672f\uff0c\u56e0\u6b64\u4e3a\u4e86\u6267\u884c\u7c7b\u4f3c\u7684\u64cd\u4f5c\uff0c\u6211\u4eec\u5fc5\u987b\u5c06\u6307\u9488\u8f6c\u6362\u4e3a\u6574\u6570\uff08\u5f53\u7136\u6709\u6574\u6570\u7b97\u672f\uff09\u3002\u4e3a\u6b64\uff0c\u6211\u4eec\u5fc5\u987b\u5c06\u6307\u9488\u8f6c\u6362\u4e3a \uff1a\u6240\u6709\u6307\u9488\u90fd\u53ef\u4ee5\u8f6c\u6362\u4e3a\u8fd9\u79cd\u7c7b\u578b\uff0c\u5e76\u4e14 unsafe.pointer<\/code> \u53ef\u4ee5\u8f6c\u6362\u4e3a uintptr<\/code> \uff08\u8fd9\u662f\u4e00\u4e2a\u65e0\u7b26\u53f7\u6574\u6570\uff0c\u8db3\u591f\u5927\u4ee5\u5b58\u50a8\u6307\u9488\u503c\u7684\u672a\u89e3\u91ca\u4f4d\uff09 \uff0c\u4f5c\u4e3a\u4e00\u4e2a\u6574\u6570\uff0c\u6211\u4eec\u53ef\u4ee5\u5bf9\u5176\u8fdb\u884c\u6574\u6570\u7b97\u672f\u3002<\/p>\n
    \u6211\u4eec\u4f7f\u7528\u503c uintptr(alignsize-1)<\/code> \u6309\u4f4d and\u3002\u7531\u4e8e alignsize<\/code> \u662f 2 \u7684\u5e42\uff08\u5305\u542b\u5355\u4e2a 1<\/code> \u4f4d\uff0c\u540e\u8ddf\u96f6\uff09\uff0c\u56e0\u6b64\u5c11\u4e00\u7684\u6570\u5b57\u662f\u5176\u4e8c\u8fdb\u5236\u8868\u793a\u5f62\u5f0f\u5168\u662f 1 \u7684\u6570\u5b57\uff0c\u4e0e alignsize<\/code> \u7684\u5c3e\u968f\u96f6\u4e00\u6837\u591a\u3002\u8bf7\u53c2\u9605\u6b64\u793a\u4f8b\uff1a<\/p>\n
    x := 0b1010101110101010101\nfmt.printf(\"alignsize   : %22b\\n\", alignsize)\nfmt.printf(\"alignsize-1 : %22b\\n\", alignsize-1)\nfmt.printf(\"x           : %22b\\n\", x)\nfmt.printf(\"result of & : %22b\\n\", x&(alignsize-1))<\/pre>\n
    \u8f93\u51fa\uff1a<\/p>\n
    alignsize   :          1000000000000\nalignsize-1 :           111111111111\nx           :    1010101110101010101\nresult of & :           110101010101<\/pre>\n
    \u56e0\u6b64\uff0c&<\/code> \u7684\u7ed3\u679c\u662f\u504f\u79fb\u91cf\uff0c\u5982\u679c\u4ece alignsize<\/code> \u4e2d\u51cf\u53bb\u8be5\u504f\u79fb\u91cf\uff0c\u60a8\u5c06\u5f97\u5230\u4e00\u4e2a\u4e0e alignsize<\/code> \u672c\u8eab\u4e00\u6837\u591a\u7684\u5c3e\u968f\u96f6\u7684\u5730\u5740\uff1a\u7ed3\u679c\u4e0e alignsize<\/code> \u7684\u500d\u6570\u201c\u5bf9\u9f50\u201d\u3002<\/p>\n
    \u56e0\u6b64\uff0c\u6211\u4eec\u5c06\u4f7f\u7528\u4ece offset<\/code> \u5f00\u59cb\u7684 file<\/code> \u5207\u7247\u90e8\u5206\uff0c\u5e76\u4e14\u6211\u4eec\u53ea\u9700\u8981 blocksize<\/code>\uff1a<\/p>\n
    file = file[offset : offset+blocksize]<\/pre>\n
    \u7f16\u8f91\uff1a<\/strong><\/p>\n
    \u67e5\u770b\u60a8\u4fee\u6539\u540e\u7684\u4ee3\u7801\u5e76\u5c1d\u8bd5\u6253\u5370\u6b65\u9aa4\uff1a\u6211\u5f97\u5230\u5982\u4e0b\u8f93\u51fa\uff1a<\/p>\n
    pointer:  0xc0000b6000\nunsafe pointer:  0xc0000b6000\nunsafe pointer, uintptr:  824634466304\nunpersand:  0\ncast to int:  0\nreturn is:  0\ncontent is:<\/pre>\n
    \u8bf7\u6ce8\u610f\uff0c\u6b64\u5904\u6ca1\u6709\u4efb\u4f55\u66f4\u6539\u3002\u7b80\u5355\u5730\u8bf4\uff0c \u5305\u4f7f\u7528\u5341\u516d\u8fdb\u5236\u8868\u793a\u6253\u5370\u6307\u9488\u503c\uff0c\u524d\u7f00\u4e3a 0x<\/code>\u3002 uintptr<\/code> \u503c\u4f7f\u7528\u5341\u8fdb\u5236\u8868\u793a\u5f62\u5f0f\u6253\u5370\u4e3a\u6574\u6570\u3002\u8fd9\u4e9b\u503c\u662f\u76f8\u7b49\u7684\uff1a<\/p>\n
    fmt.Println(0xc0000b6000, 824634466304) \/\/ output: 824634466304 824634466304<\/pre>\n
    \u8fd8\u8981\u6ce8\u610f\u5176\u4f59\u7684\u662f0<\/code>\uff0c\u56e0\u4e3a\u5728\u6211\u7684\u4f8b\u5b50\u4e2d0xc0000b6000<\/code>\u5df2\u7ecf\u662f4096<\/code>\u7684\u500d\u6570\uff0c\u5728\u4e8c\u8fdb\u5236\u4e2d\u5b83\u662f110000000000000000010000111000000000000 0<\/code>\u3002<\/p>\n
    \u7f16\u8f91#2\uff1a<\/strong><\/p>\n
    \u5f53\u60a8\u4f7f\u7528 fmt.println()<\/code> \u8c03\u8bd5\u90e8\u5206\u8ba1\u7b97\u65f6\uff0c\u53ef\u80fd\u4f1a\u66f4\u6539\u9003\u9038\u5206\u6790\u5e76\u53ef\u80fd\u66f4\u6539\u5207\u7247\u7684\u5206\u914d\uff08\u4ece\u5806\u6808\u5230\u5806\uff09\u3002\u8fd9\u4e5f\u53d6\u51b3\u4e8e\u6240\u4f7f\u7528\u7684 go \u7248\u672c\u3002\u4e0d\u8981\u4f9d\u8d56\u4e8e\u5728\uff08\u5df2\u7ecf\uff09\u4e0e alignsize<\/code> \u5bf9\u9f50\u7684\u5730\u5740\u5206\u914d\u60a8\u7684\u5207\u7247\u3002<\/p>\n
    \u6709\u5173\u66f4\u591a\u8be6\u7ec6\u4fe1\u606f\uff0c\u8bf7\u53c2\u9605\u76f8\u5173\u95ee\u9898\uff1a<\/p>\n<\/p>\n<\/p>\n
    \u4ee5\u4e0a\u5c31\u662f\u300a\u8fd9\u6bb5\u4ee3\u7801\u5982\u4f55\u751f\u6210\u5185\u5b58\u5bf9\u9f50\u7684\u5207\u7247\uff1f\u300b\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u5173\u4e8e\u7684\u8d44\u6599\u8bf7\u5173\u6ce8\u516c\u4f17\u53f7\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u5f53\u524d\u4f4d\u7f6e\uff1a > > ...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4925],"tags":[],"class_list":["post-207540","post","type-post","status-publish","format-standard","hentry","category-4925"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/207540","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=207540"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/207540\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=207540"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=207540"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=207540"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}