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