please give explanaition from devicedriver second edition book from oreilly - Linux

This is a discussion on please give explanaition from devicedriver second edition book from oreilly - Linux ; Hi all, following is the text from linux device driver - 2nd edition from orelly publication. it is chaper number -3 ( http://www.or eilly.com/catalog/linuxdrive2/chapter/bookindexpdf.html.) CHARACTER DRIVER. on page number 21 they have given figure 3-1. i count copy figure over ...

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  1. please give explanaition from devicedriver second edition book from oreilly

    Hi all,

    following is the text from linux device driver - 2nd edition from
    orelly publication. it is chaper number -3 (http://www.or
    eilly.com/catalog/linuxdrive2/chapter/bookindexpdf.html.) CHARACTER
    DRIVER. on page number 21 they have given figure 3-1. i count copy
    figure over here.

    problem statement: The chosen numbers are such that writing a single
    byte in scull consumes eight or twelve thousand bytes of memory: four
    thousand for the quantum and four or eight thousand for the quantum set


    Question: How come signle byte consume eight or twelve thousand bytes?
    please expain me this if possible

    thanks in advance
    dharmendra

    following is the book content:

    In scull, each device is a linked list of pointers, each of
    which points to a
    Scull_Dev structur e. Each such structure can refer, by default, to at
    most four
    million bytes, through an array of intermediate pointers. The released
    source uses
    an array of 1000 pointers to areas of 4000 bytes. We call each memory
    area a
    quantum and the array (or its length) a quantum set. A scull device and
    its memory
    areas are shown in Figure 3-1.

    figure is here( it is given on page
    number 21 )

    The chosen numbers are such that writing a single byte in scull
    consumes eight or
    twelve thousand bytes of memory: four thousand for the quantum and four
    or
    eight thousand for the quantum set (according to whether a pointer is
    repr esented
    in 32 bits or 64 bits on the target platform). If, instead, you write a
    huge amount of
    data, the overhead of the linked list is not too bad. There is only one
    list element
    for every four megabytes of data, and the maximum size of the device is
    limited
    by the computer's memory size.


  2. Re: please give explanaition from devicedriver second edition book from oreilly


    Dharmendra wrote:

    > Hi all,
    >
    > following is the text from linux device driver - 2nd edition from
    > orelly publication. it is chaper number -3 (http://www.or
    > eilly.com/catalog/linuxdrive2/chapter/bookindexpdf.html.) CHARACTER
    > DRIVER. on page number 21 they have given figure 3-1. i count copy
    > figure over here.
    >
    > problem statement: The chosen numbers are such that writing a single
    > byte in scull consumes eight or twelve thousand bytes of memory: four
    > thousand for the quantum and four or eight thousand for the quantum set
    >
    >
    > Question: How come signle byte consume eight or twelve thousand bytes?
    > please expain me this if possible
    >

    The implementation chosen for scull is not a smart one. The source code
    for a smart implementation would be more difficult to read, and the aim
    of this section is to show read and write, not memory management. .
    (from same page)
    > thanks in advance
    > dharmendra
    >
    > following is the book content:
    >
    > In scull, each device is a linked list of pointers, each of
    > which points to a
    > Scull_Dev structur e. Each such structure can refer, by default, to at
    > most four
    > million bytes, through an array of intermediate pointers. The released
    > source uses
    > an array of 1000 pointers to areas of 4000 bytes. We call each memory
    > area a
    > quantum and the array (or its length) a quantum set. A scull device and
    > its memory
    > areas are shown in Figure 3-1.
    >
    > figure is here( it is given on page
    > number 21 )
    >
    > The chosen numbers are such that writing a single byte in scull
    > consumes eight or
    > twelve thousand bytes of memory: four thousand for the quantum and four
    > or
    > eight thousand for the quantum set (according to whether a pointer is
    > repr esented
    > in 32 bits or 64 bits on the target platform). If, instead, you write a
    > huge amount of
    > data, the overhead of the linked list is not too bad. There is only one
    > list element
    > for every four megabytes of data, and the maximum size of the device is
    > limited
    > by the computer's memory size.



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