2ee2724a4
Denys Vlasenko
2009-10-21
Subject
mkfs_ext2: explain 256-byte inodes. no code changes
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util-linux/mkfs_ext2.c+39 -19
| @@ -120,16 +120,45 @@ static uint32_t has_super(uint32_t x) | |
| } | |
| } | |
| - | /* Standard mke2fs 1.41.9: |
| - | * Usage: mke2fs [-c|-l filename] [-b block-size] [-f fragment-size] |
| - | * [-i bytes-per-inode] [-I inode-size] [-J journal-options] |
| - | * [-G meta group size] [-N number-of-inodes] |
| - | * [-m reserved-blocks-percentage] [-o creator-os] |
| - | * [-g blocks-per-group] [-L volume-label] [-M last-mounted-directory] |
| - | * [-O feature[,...]] [-r fs-revision] [-E extended-option[,...]] |
| - | * [-T fs-type] [-U UUID] [-jnqvFSV] device [blocks-count] |
| - | */ |
| - | // N.B. not commented below options are taken and silently ignored |
| + | #define fd 3 /* predefined output descriptor */ |
| + | |
| + | static void PUT(uint64_t off, void *buf, uint32_t size) |
| + | { |
| + | // bb_info_msg("PUT[%llu]:[%u]", off, size); |
| + | xlseek(fd, off, SEEK_SET); |
| + | xwrite(fd, buf, size); |
| + | } |
| + | |
| + | // 128 and 256-byte inodes: |
| + | // 128-byte inode is described by struct ext2_inode. |
| + | // 256-byte one just has these fields appended: |
| + | // __u16 i_extra_isize; |
| + | // __u16 i_pad1; |
| + | // __u32 i_ctime_extra; /* extra Change time (nsec << 2 | epoch) */ |
| + | // __u32 i_mtime_extra; /* extra Modification time (nsec << 2 | epoch) */ |
| + | // __u32 i_atime_extra; /* extra Access time (nsec << 2 | epoch) */ |
| + | // __u32 i_crtime; /* File creation time */ |
| + | // __u32 i_crtime_extra; /* extra File creation time (nsec << 2 | epoch)*/ |
| + | // __u32 i_version_hi; /* high 32 bits for 64-bit version */ |
| + | // the rest is padding. |
| + | // |
| + | // linux/ext2_fs.h has "#define i_size_high i_dir_acl" which suggests that even |
| + | // 128-byte inode is capable of describing large files (i_dir_acl is meaningful |
| + | // only for directories, which never need i_size_high). |
| + | // |
| + | // Standard mke2fs creates a filesystem with 256-byte inodes if it is |
| + | // bigger than 0.5GB. So far, we do not do this. |
| + | |
| + | // Standard mke2fs 1.41.9: |
| + | // Usage: mke2fs [-c|-l filename] [-b block-size] [-f fragment-size] |
| + | // [-i bytes-per-inode] [-I inode-size] [-J journal-options] |
| + | // [-G meta group size] [-N number-of-inodes] |
| + | // [-m reserved-blocks-percentage] [-o creator-os] |
| + | // [-g blocks-per-group] [-L volume-label] [-M last-mounted-directory] |
| + | // [-O feature[,...]] [-r fs-revision] [-E extended-option[,...]] |
| + | // [-T fs-type] [-U UUID] [-jnqvFSV] device [blocks-count] |
| + | // |
| + | // Options not commented below are taken but silently ignored: |
| enum { | |
| OPT_c = 1 << 0, | |
| OPT_l = 1 << 1, | |
| @@ -159,15 +188,6 @@ enum { | |
| //OPT_V = 1 << 25, // -V version. bbox applets don't support that | |
| }; | |
| - | #define fd 3 /* predefined output descriptor */ |
| - | |
| - | static void PUT(uint64_t off, void *buf, uint32_t size) |
| - | { |
| - | // bb_info_msg("PUT[%llu]:[%u]", off, size); |
| - | xlseek(fd, off, SEEK_SET); |
| - | xwrite(fd, buf, size); |
| - | } |
| - | |
| int mkfs_ext2_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; | |
| int mkfs_ext2_main(int argc UNUSED_PARAM, char **argv) | |
| { | |