Re: [PATCH 1/2] mm: move common segment checks to separate helper function (v6)

Dmitriy Monakhov
2007-03-12T18:32:16Z

Nick Piggin <npiggin@suse.de> writes:

> On Mon, Mar 12, 2007 at 10:57:53AM +0300, Dmitriy Monakhov wrote:
>> I realy don't want to be annoying by sending this patcheset over and over
>> again. If anyone think this patch is realy cappy, please comment what
>> exectly is bad. Thank you.
>
> Doesn't seem like a bad idea.
>
>>
>> Changes:
>> - patch was split in two patches.

>> +/*
>> + * Performs necessary checks before doing a write
>> + *
>> + * Adjust number of segments and amount of bytes to write.
>> + * Returns appropriate error code that caller should return or
>> + * zero in case that write should be allowed.
>> + */
>> +inline int generic_segment_checks(const struct iovec *iov,
>> + unsigned long *nr_segs, size_t *count,
>> + unsigned long access_flags)
>
> Make it static and not inline, and the compiler will work it out.
Wow i've just carefully checked and found more functions with duplicating code:
fs/xfs/linux-2.6/xfs_lrw.c:655 xfs_write()
fs/ntfs/file.c:2339 ntfs_file_aio_write_nolock()
So i think nobody will object against exporting generic_segment_checks()
and removing doplicating code.
>
> This function name doesn't really imply that it returns you the
> nr_segs and count, but that's not a big deal I guess.
>
> You also don't say that nr_segs should be initialised to the amount
> you which to write, while count must be initialised to zero.
>
>> +{
>> + unsigned long seg;
>> + for (seg = 0; seg < *nr_segs; seg++) {
>> + const struct iovec *iv = &iov[seg];
>> +
>> + /*
>> + * If any segment has a negative length, or the cumulative
>> + * length ever wraps negative then return -EINVAL.
>> + */
>> + *count += iv->iov_len;
>> + if (unlikely((ssize_t)(*count|iv->iov_len) < 0))
>> + return -EINVAL;
>> + if (access_ok(access_flags, iv->iov_base, iv->iov_len))
>> + continue;
>
> Why now insert the above test, and put the below statements inside the
> branch? OTOH, that makes it less obviously c&p from the others. Maybe
> a subsequent patch.
>
>> + if (seg == 0)
>> + return -EFAULT;
>> + *nr_segs = seg;
>> + *count -= iv->iov_len; /* This segment is no good */
>> + break;
>> + }
>
>
> You could assign to *count here, once, and remove the requirement
> that the caller initialised it to zero?
>
>> + return 0;
>> +}
>> +
>> /**
>> * generic_file_aio_read - generic filesystem read routine
>> * @iocb: kernel I/O control block
>> @@ -1180,24 +1213,9 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>> loff_t *ppos = &iocb->ki_pos;
>>
>> count = 0;
>> - for (seg = 0; seg < nr_segs; seg++) {
>> - const struct iovec *iv = &iov[seg];
>> -
>> - /*
>> - * If any segment has a negative length, or the cumulative
>> - * length ever wraps negative then return -EINVAL.
>> - */
>> - count += iv->iov_len;
>> - if (unlikely((ssize_t)(count|iv->iov_len) < 0))
>> - return -EINVAL;
>> - if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
>> - continue;
>> - if (seg == 0)
>> - return -EFAULT;
>> - nr_segs = seg;
>> - count -= iv->iov_len; /* This segment is no good */
>> - break;
>> - }
>> + retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
>> + if (retval)
>> + return retval;
>>
>> /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
>> if (filp->f_flags & O_DIRECT) {
>> @@ -2094,30 +2112,14 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
>> size_t ocount; /* original count */
>> size_t count; /* after file limit checks */
>> struct inode *inode = mapping->host;
>> - unsigned long seg;
>> loff_t pos;
>> ssize_t written;
>> ssize_t err;
>>
>> ocount = 0;
>> - for (seg = 0; seg < nr_segs; seg++) {
>> - const struct iovec *iv = &iov[seg];
>> -
>> - /*
>> - * If any segment has a negative length, or the cumulative
>> - * length ever wraps negative then return -EINVAL.
>> - */
>> - ocount += iv->iov_len;
>> - if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
>> - return -EINVAL;
>> - if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
>> - continue;
>> - if (seg == 0)
>> - return -EFAULT;
>> - nr_segs = seg;
>> - ocount -= iv->iov_len; /* This segment is no good */
>> - break;
>> - }
>> + err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
>> + if (err)
>> + return err;
>>
>> count = ocount;
>> pos = *ppos;
>> --
>> 1.5.0.1
>>
> -
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