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    Subject[PATCH 05/10] drivers/char: Support compiling out /dev/zero
    Date
    Some embedded systems with tightly controlled userspace have no use
    for /dev/zero, and could benefit from the size savings gained by
    omitting it. Add a new EMBEDDED config option to disable it.

    bloat-o-meter (based on tinyconfig):

    add/remove: 0/3 grow/shrink: 0/1 up/down: 0/-391 (-391)
    function old new delta
    chr_dev_init 162 147 -15
    mmap_zero 16 - -16
    zero_fops 116 - -116
    zero_bdi 244 - -244

    Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    ---
    drivers/char/Kconfig | 10 ++++++++++
    drivers/char/mem.c | 15 +++++++++++----
    2 files changed, 21 insertions(+), 4 deletions(-)

    diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
    index 17f6ddf..00f9b8a 100644
    --- a/drivers/char/Kconfig
    +++ b/drivers/char/Kconfig
    @@ -46,6 +46,16 @@ config DEVNULL
    systems with strictly controlled userspace may not need it.
    When in doubt, say "Y".

    +config DEVZERO
    + bool "/dev/zero virtual device support" if EMBEDDED
    + depends on DEVMEM_BASE
    + default y
    + help
    + Say Y here if you want to support the /dev/zero device. The
    + /dev/zero device is used by many programs, but some embedded
    + systems with strictly controlled userspace may not need it.
    + When in doubt, say "Y".
    +
    config SGI_SNSC
    bool "SGI Altix system controller communication support"
    depends on (IA64_SGI_SN2 || IA64_GENERIC)
    diff --git a/drivers/char/mem.c b/drivers/char/mem.c
    index 25d6f5b..96f7a9d 100644
    --- a/drivers/char/mem.c
    +++ b/drivers/char/mem.c
    @@ -633,7 +633,8 @@ static ssize_t __maybe_unused aio_write_null(struct kiocb *iocb,
    return iov_length(iov, nr_segs);
    }

    -static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
    +static ssize_t __maybe_unused read_iter_zero(struct kiocb *iocb,
    + struct iov_iter *iter)
    {
    size_t written = 0;

    @@ -652,6 +653,7 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
    return written;
    }

    +#ifdef CONFIG_DEVZERO
    static int mmap_zero(struct file *file, struct vm_area_struct *vma)
    {
    #ifndef CONFIG_MMU
    @@ -661,6 +663,7 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma)
    return shmem_zero_setup(vma);
    return 0;
    }
    +#endif

    static ssize_t write_full(struct file *file, const char __user *buf,
    size_t count, loff_t *ppos)
    @@ -767,6 +770,7 @@ static const struct file_operations port_fops = {
    };
    #endif

    +#ifdef CONFIG_DEVZERO
    static const struct file_operations zero_fops = {
    .llseek = zero_lseek,
    .read = new_sync_read,
    @@ -785,6 +789,7 @@ static struct backing_dev_info zero_bdi = {
    .name = "char/mem",
    .capabilities = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
    };
    +#endif

    static const struct file_operations full_fops = {
    .llseek = full_lseek,
    @@ -811,7 +816,9 @@ static const struct memdev {
    #ifdef CONFIG_DEVPORT
    [4] = { "port", 0, &port_fops, NULL },
    #endif
    +#ifdef CONFIG_DEVZERO
    [5] = { "zero", 0666, &zero_fops, &zero_bdi },
    +#endif
    [7] = { "full", 0666, &full_fops, NULL },
    [8] = { "random", 0666, &random_fops, NULL },
    [9] = { "urandom", 0666, &urandom_fops, NULL },
    @@ -864,12 +871,12 @@ static struct class *mem_class;
    static int __init chr_dev_init(void)
    {
    int minor;
    - int err;

    - err = bdi_init(&zero_bdi);
    +#ifdef CONFIG_DEVZERO
    + int err = bdi_init(&zero_bdi);
    if (err)
    return err;
    -
    +#endif
    if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
    printk("unable to get major %d for memory devs\n", MEM_MAJOR);

    --
    1.9.3


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