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vfs/block: fix seek-offset handling during write

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The block file system wrongly modified the seek offset during a
read-modify-write operation that is required for sub-block-size
requests. This led to problems whenever such write requests spanned
multiple blocks and thereby were handled in multiple iterations.

Fixes #2262
This commit is contained in:
Norman Feske 2017-01-28 18:33:33 +01:00
parent c65f78671f
commit 818795ab90
1 changed files with 8 additions and 12 deletions
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20
repos/os/src/lib/vfs/block_file_system.h
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@ -205,12 +205,12 @@ class Vfs::Block_file_system : public Single_file_system
nbytes = _block_io(blk_nr, (void*)(buf + written),
bytes_left, true, true);
if (nbytes == 0) {
Genode::error("error while write block:", blk_nr, " from block device");
Genode::error("error while write block:", blk_nr, " to block device");
return WRITE_ERR_INVALID;
}
written += nbytes;
count -= nbytes;
written += nbytes;
count -= nbytes;
seek_offset += nbytes;
continue;
@ -223,23 +223,19 @@ class Vfs::Block_file_system : public Single_file_system
* write the whole block back. In addition if length is less
* than block size, we also have to read the block first.
*/
if (displ > 0 || length < _block_size) {
if (displ > 0 || length < _block_size)
_block_io(blk_nr, _block_buffer, _block_size, false);
/* rewind seek offset to account for the block read */
seek_offset -= _block_size;
}
Genode::memcpy(_block_buffer + displ, buf + written, length);
nbytes = _block_io(blk_nr, _block_buffer, _block_size, true);
if ((unsigned)nbytes != _block_size) {
Genode::error("error while writing block:", blk_nr, " to Block_device");
Genode::error("error while writing block:", blk_nr, " to block_device");
return WRITE_ERR_INVALID;
}
written += length;
count -= length;
written += length;
count -= length;
seek_offset += length;
}
@ -273,7 +269,7 @@ class Vfs::Block_file_system : public Single_file_system
length = count;
/*
* We take a shortcut and read the blocks all at once if t he
* We take a shortcut and read the blocks all at once if the
* offset is aligned on a block boundary and we the count is a
* multiple of the block size, e.g. 4K reads will be read at
* once.