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推广类软文,直通车关键词怎么优化,网站建设要准备什么,建设学习网站前言 在之前 ls 命令 中我们可以看到, ls 命令的执行也是依赖于 opendir, readdir, stat, lstat 等相关操作系统提供的相关系统调用来处理业务 因此 我们这里来进一步看一下 更细节的这些 系统调用 我们这里关注的是 readdir 这个函数, 入口系统调用是 getdents 如下调试…

前言

在之前 ls 命令 中我们可以看到, ls 命令的执行也是依赖于 opendir, readdir, stat, lstat 等相关操作系统提供的相关系统调用来处理业务 

因此 我们这里来进一步看一下 更细节的这些 系统调用 

我们这里关注的是 readdir 这个函数, 入口系统调用是 getdents 

如下调试基于命令 "ls -l /jerry"

如下调试基于 linux 4.10

readdir 的词条 

getdents 

封装 getdents_callback, 然后 迭代 f 中的各个文件, getdents_callback 中藏有回调 

将数据最终存放于 buf 中 

ext4_dx_readdir

如下图 第一个 if block 为填充 info 用于迭代, 大致的工作是 将当前文件夹下的各个文件的相关信息填充到 info.root 中

然后 后面的处理为 迭代 info.root 的整棵树, 然后调用 call_filldir 来填充各个文件的信息, call_filldir 中会委托调用上面的 getdents_callback.ctx.actor 

htree_dirblock_to_tree

如下会 迭代 dir 中的各个文件, 然后调用 ext4_htree_store_dirent 将各个文件的信息放到 info.root 中

ext4_htree_store_dirent 

复制给定的文件的相关信息到 info.root 

这个 info.root 是基于 file->private_data 进行传输的, 具体的外面处理是在 ext4_dx_readdir 函数中

这里是 获取当前节点的 hash, minor_hash, inode, name, name_len, file_type 封装到 fname 中, 然后插入到 info.root[红黑树], 根据 hash, minor_hash 进行排序 

关于这个顺序, 我们待会儿会有一个 case 来论证

call_filldir

接着来到外部 ext4_dx_readdir 中, 迭代目录中的各个文件信息, 调用回调填充 数据到 buf

filldir 

调用 filldir 向 buf.current_dir 中填充当前 dir 的各个文件信息 

这个 buf.current_dir 是从参数传入的一个 用户空间的 dirent, 因此 这里使用了 __put_user 函数 

这里向 dirent 中填充了 inode_no, record_len, d->name, 0[字符串结束符], file_type, offset 等相关信息 

我们来看一下 填充之后的相关信息 

内存中的数据 可以对号入座一下, 这里 省略 

(gdb) x /30bc 0xaa3a40
0xaa3a40:	18 '\022'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'
0xaa3a48:	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'	0 '\000'
0xaa3a50:	32 ' '	0 '\000'	84 'T'	101 'e'	115 's'	116 't'	48 '0'	50 '2'
0xaa3a58:	77 'M'	97 'a'	108 'l'	108 'l'	111 'o'	99 'c'

确认一下 Test02Malloc 的 inode_no, 确实是 18 

(initramfs) ls -ail /jerry/29 -rwxr-xr-x    1      8912 Test19UdpClient0232 -rw-r--r--    1       860 Test19UdpServer.c21 -rw-r--r--    1      1036 Test05SocketClient.c12 -rw-r--r--    1         7 1.txt35 -rw-r--r--    1         2 4.txt16 -rwxr-xr-x    1    913944 Test01SumStatic22 -rwxr-xr-x    1      9232 Test05SocketServer14 -rwxr-xr-x    1      9784 Test01Sum11 drwx------    2     12288 lost+found2 drwxr-xr-x    3      1024 .25 -rw-r--r--    1      2213 Test18UdpClient.c30 -rw-r--r--    1       790 Test19UdpClient.c28 -rwxr-xr-x    1      8912 Test19UdpClient24 -rwxr-xr-x    1     13656 Test18UdpClient13 -rwxr-xr-x    1     44168 ping23 -rw-r--r--    1      1839 Test05SocketServer.c34 -rw-r--r--    1         2 3.txt17 -rw-r--r--    1      8828 Test01Sum.txt19 -rw-r--r--    1       112 Test02Malloc.c36 -rw-r--r--    1         0 2.xml1 drwxr-xr-x   18         0 ..33 -rw-r--r--    1         2 2.txt31 -rwxr-xr-x    1      9008 Test19UdpServer20 -rwxr-xr-x    1      9208 Test05SocketClient15 -rw-r--r--    1       127 Test01Sum.c27 -rw-r--r--    1      2139 Test18UdpServer.c26 -rwxr-xr-x    1     13656 Test18UdpServer18 -rwxr-xr-x    1      9898 Test02Malloc
(initramfs)

回顾一下 ls 中的使用

使用的是 系统调用获取到的 file_type, file_name, inode_no 等等 

readdir 中获取的文件顺序

如下 摘录出 /jerry 中各个文件, 以及其 hash 

然后根据 hash 进行排序, 输出各个文件的顺序, 我们比较一下 和 "ls -l /jerry" 的顺序的一下关系, 联系 

/*** Test13ResolveFileAndHash** @author Jerry.X.He <970655147@qq.com>* @version 1.0* @date 2022-08-06 10:58*/
public class Test13ResolveFileAndHash {// Test13ResolveFileAndHashpublic static void main(String[] args) {String lines = "(gdb) printf \"%s %ld\", ent_name->name, hash\n" +". 2361201130\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=1798131950, minor_hash=3795156168, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +".. 1798131950\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2638309314, minor_hash=220112255, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"lost+found 2638309314\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=4147007512, minor_hash=1467808689, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"1.txt 4147007512\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2218817754, minor_hash=2900089684, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"ping\u000E 2218817754\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2722591116, minor_hash=3228507950, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Test01Sum 2722591116\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=582633220, minor_hash=3262287479, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Test01Sum.c 582633220\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=3631608018, minor_hash=2725415301, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Test01SumStatic 3631608018\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2142992528, minor_hash=928223017, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Test01Sum.txt 2142992528\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=220227180, minor_hash=2471538305, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Test02Malloc\u0013 220227180\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=1840751322, minor_hash=137392396, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"(gdb) printf \"%s %ld\", ent_name->name, hash\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=857331192, minor_hash=434642936, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test05SocketClient 857331192\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=4158704484, minor_hash=312643960, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test05SocketClient.c\u0016 4158704484\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=3462659828, minor_hash=2883930437, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test05SocketServer 3462659828\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2205009970, minor_hash=314116339, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test05SocketServer.c\u0018 2205009970\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2263127060, minor_hash=2266183803, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test18UdpClient 2263127060\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2342703042, minor_hash=2944388140, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test18UdpClient.c 2342703042\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=428460190, minor_hash=2134201002, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test18UdpServer 428460190\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=493987328, minor_hash=2169830099, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test18UdpServer.c 493987328\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2302229242, minor_hash=322069301, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test19UdpClient 2302229242\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=4262479554, minor_hash=1848801320, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test19UdpClient02 4262479554\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2304662458, minor_hash=1793028086, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test19UdpClient.c 2304662458\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=888054094, minor_hash=304564512, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test19UdpServer 888054094\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=4198063328, minor_hash=3673609025, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"Test19UdpServer.c 4198063328\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=1673380854, minor_hash=394531314, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"2.txt 1673380854\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=2170292718, minor_hash=758117636, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"3.txt 2170292718\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=4053642864, minor_hash=2642363966, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"4.txt 4053642864\n" +"Breakpoint 6, ext4_htree_store_dirent (dir_file=<optimized out>, hash=1832402012, minor_hash=2399099147, dirent=<optimized out>, ent_name=0xffffc9000074bcb8) at fs/ext4/dir.c:459\n" +"459\t\tnew_fn->name[ent_name->len] = 0;\n" +"2.xml 1832402012 \n";Map<Long, String> hash2FileName = new TreeMap<>();for (String line : lines.split("\n")) {if (line.contains("ext4_htree_store_dirent")) {continue;}if (line.contains("new_fn->name")) {continue;}if (line.contains("printf")) {continue;}//            System.out.println(line);String[] splits = line.split("\\s+");hash2FileName.put(Long.parseLong(splits[1]), splits[0]);}for (Map.Entry<Long, String> entry : hash2FileName.entrySet()) {System.out.println(entry.getValue());}}}

文件顺序如下, 呵呵 是不是和 "ls -l /jerry" 的顺序差不多, 只是顺序是反的 

从 readdir 中读取的文件的顺序和 上面的 Test13ResolveFileAndHash 的顺序一致, 那就是 外围的 ls 的处理可能导致的这个顺序上的差异 

类似于 coreutils 中 ls 是有 根据文件名排序, 根据扩展名排序, 根据文件大小排序, 根据版本排序, 根据时间排序

只是 qemu虚拟机中的 ls 的排序 是另外一种排序, 并且有一些 奇怪 

Test02Malloc
Test18UdpServer
Test18UdpServer.c
Test01Sum.c
Test05SocketClient
Test19UdpServer
2.txt
..
2.xml
Test01Sum.txt
3.txt
Test05SocketServer.c
ping
Test18UdpClient
Test19UdpClient
Test19UdpClient.c
Test18UdpClient.c
.
lost+found
Test01Sum
Test05SocketServer
Test01SumStatic
4.txt
1.txt
Test05SocketClient.c
Test19UdpServer.c
Test19UdpClient02

readdir 的顺序, 抽样前两个 

 

"ls -ail /jerry" 的顺序

(initramfs) ls -ail /jerry29 -rwxr-xr-x    1      8912 Test19UdpClient0232 -rw-r--r--    1       860 Test19UdpServer.c21 -rw-r--r--    1      1036 Test05SocketClient.c12 -rw-r--r--    1         7 1.txt35 -rw-r--r--    1         2 4.txt16 -rwxr-xr-x    1    913944 Test01SumStatic22 -rwxr-xr-x    1      9232 Test05SocketServer14 -rwxr-xr-x    1      9784 Test01Sum11 drwx------    2     12288 lost+found2 drwxr-xr-x    3      1024 .25 -rw-r--r--    1      2213 Test18UdpClient.c30 -rw-r--r--    1       790 Test19UdpClient.c28 -rwxr-xr-x    1      8912 Test19UdpClient24 -rwxr-xr-x    1     13656 Test18UdpClient13 -rwxr-xr-x    1     44168 ping23 -rw-r--r--    1      1839 Test05SocketServer.c34 -rw-r--r--    1         2 3.txt17 -rw-r--r--    1      8828 Test01Sum.txt19 -rw-r--r--    1       112 Test02Malloc.c36 -rw-r--r--    1         0 2.xml1 drwxr-xr-x   18         0 ..33 -rw-r--r--    1         2 2.txt31 -rwxr-xr-x    1      9008 Test19UdpServer20 -rwxr-xr-x    1      9208 Test05SocketClient15 -rw-r--r--    1       127 Test01Sum.c27 -rw-r--r--    1      2139 Test18UdpServer.c26 -rwxr-xr-x    1     13656 Test18UdpServer18 -rwxr-xr-x    1      9898 Test02Malloc

调试虚拟机 ls 命令帮助文档如下 

(initramfs) ls -help
ls: invalid option -- 'h'
BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) multi-call binary.Usage: ls [-1AaCxdLHFplins] [FILE]...List directory contents-1	One column output-a	Include entries which start with .-A	Like -a, but exclude . and ..-C	List by columns-x	List by lines-d	List directory entries instead of contents-L	Follow symlinks-H	Follow symlinks on command line-p	Append / to dir entries-F	Append indicator (one of */=@|) to entries-l	Long listing format-i	List inode numbers-n	List numeric UIDs and GIDs instead of names-s	List allocated blocks

呵呵 从宿主机 ubuntu 拿到的顺序又不一样 

root@ubuntu:/jerryDisk/linux-4.10.14# ls -ail images/share/
total 10752 drwxr-xr-x 3 root root   1024 May  4 00:57 .
414752 drwxr-xr-x 5 root root   4096 May  4 00:58 ..12 -rw-r--r-- 1 root root      7 May  4 00:57 1.txt33 -rw-r--r-- 1 root root      2 Jul 30 19:03 2.txt36 -rw-r--r-- 1 root root      0 Jul 30 20:13 2.xml34 -rw-r--r-- 1 root root      2 Jul 30 19:03 3.txt35 -rw-r--r-- 1 root root      2 Jul 30 19:03 4.txt14 -rwxr-xr-x 1 root root   9784 May  4 00:57 Test01Sum15 -rw-r--r-- 1 root root    127 May  4 00:57 Test01Sum.c17 -rw-r--r-- 1 root root   8828 May  4 00:57 Test01Sum.txt16 -rwxr-xr-x 1 root root 913944 May  4 00:57 Test01SumStatic18 -rwxr-xr-x 1 root root   9898 Jul 30 19:05 Test02Malloc19 -rw-r--r-- 1 root root    112 May  4 00:57 Test02Malloc.c20 -rwxr-xr-x 1 root root   9208 May  4 00:57 Test05SocketClient21 -rw-r--r-- 1 root root   1036 May  4 00:57 Test05SocketClient.c22 -rwxr-xr-x 1 root root   9232 May  4 00:57 Test05SocketServer23 -rw-r--r-- 1 root root   1839 May  4 00:57 Test05SocketServer.c24 -rwxr-xr-x 1 root root  13656 May  4 00:57 Test18UdpClient25 -rw-r--r-- 1 root root   2213 May  4 00:57 Test18UdpClient.c26 -rwxr-xr-x 1 root root  13656 May  4 00:57 Test18UdpServer27 -rw-r--r-- 1 root root   2139 May  4 00:57 Test18UdpServer.c28 -rwxr-xr-x 1 root root   8912 May  4 00:57 Test19UdpClient30 -rw-r--r-- 1 root root    790 May  4 00:57 Test19UdpClient.c29 -rwxr-xr-x 1 root root   8912 May  4 00:57 Test19UdpClient0231 -rwxr-xr-x 1 root root   9008 May  4 00:57 Test19UdpServer32 -rw-r--r-- 1 root root    860 May  4 00:57 Test19UdpServer.c11 drwx------ 2 root root  12288 May  4 00:56 lost+found13 -rwxr-xr-x 1 root root  44168 May  4 00:57 ping

上面提到的 hash 的计算方式存在于 hash.ext4fs_dirhash 中

readdir/ls 中的文件顺序关联的问题?

可以关联到如下问题中的 "WebappClassloader 如何加载 ?", 它的类加载顺序 依赖于 File.list 

40 classpath中存在多个jar存在同限定名的class classloader会如何加载_蓝风9的博客-CSDN博客_xbootclasspath 多个jar

File.list 实现来自于 FileSystem.list 

其实现 也取决于 readdir 相关具体的实现 

完 

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