Nir Tzachar wrote:
On Wed, 2005-07-20 at 20:14 -0700, Badari Pulavarty wrote:
Nir Tzachar wrote:
hello list.
can someone please explain the exact semantics the get_block_t function
(which is passed to mpage_readpage(s)) should implement??
i could not find any documentation, and existing code kind of baffled
me...
my current understanding goes like this:
if the block is present, call map_bh on the bh, with the physical block
number.
else, if "create" is set, allocate a new block for the inode, and again
update the new physical block number.
is this all??
thanks.
For a given file offset, get_block() function is supposed to return the
physical disk block# of the block. (and size of the block). If "create"
is one, it needs to allocate the block (if it doesn't already exist).
Makes sense ?
from fs.h:
typedef int (get_block_t)(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create);
so, iblock is the block number in the file, or the offset in the file??
iblock = fileoffset in represented sectors. (for example,
file offset 4K = 8)
furthermore, what set_buffer_mapped (used in map_bh) does?? i could not
find it's definition anywhere??
When the filesystems map the fileoffset to a disk block, it returns the
block# in the "bh->b_blocknr" and sets the flag to indicate that the
buffer is mapped (to a disk block).
If get_block() returned sucess, but if the buffer mapped is not set,
means thats there is a hole.
about create, "allocate a block" means just deciding which block should
be allocated, update the fs control structures, and return that block #,
right??
yep.
Thanks,
Badari
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