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btrfs-progs: Document logic of btrfs_read_dev_super 

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
master
Nikolay Borisov 2017-12-05 10:39:47 +02:00 committed by David Sterba
parent 8075fd4da1
commit 90a16b10b3
1 changed files with 17 additions and 0 deletions
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17
disk-io.c
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@ -1419,6 +1419,23 @@ error_out:
return -EIO;
}
/*
* btrfs_read_dev_super - read a valid superblock from a block device
* @fd: file descriptor of the device
* @sb: buffer where the superblock is going to be read in
* @sb_bytenr: offset of the particular superblock copy we want
* @sbflags: flags controlling how the superblock is read
*
* This function is used by various btrfs comands to obtain a valid superblock.
*
* It's mode of operation is controlled by the @sb_bytenr and @sbdflags
* parameters. If SBREAD_RECOVER flag is set and @sb_bytenr is
* BTRFS_SUPER_INFO_OFFSET then the function reads all 3 superblock copies and
* returns the newest one. If SBREAD_RECOVER is not set then only a single
* copy is read, which one is decided by @sb_bytenr. If @sb_bytenr !=
* BTRFS_SUPER_INFO_OFFSET then the @sbflags is effectively ignored and only a
* single copy is read.
*/
int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr,
unsigned sbflags)
{