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A few more changes to pages_io():

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* Added a few comments.
* Simplified the nested while loops by dropping the special handling for the
  first iovec and restructuring the innermost loop. This also rules out
  the possibility of a zero-length temporary vec. IMHO the readability
  has improved quite a bit (YMMV :-). Hopefully without introducing new
  bugs; please review!
* Corrected computation of totalSize in case less than size has been
  read/written.
* Also set *_numBytes in case all fileVecs have been processed. Only
  relevant in case the request extends beyond the end of file.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20483 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Ingo Weinhold 2007-03-31 22:44:01 +00:00
parent 08e7fb4054
commit 57a860987a
1 changed files with 29 additions and 24 deletions
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53
src/system/kernel/cache/file_cache.cpp vendored
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@ -415,37 +415,41 @@ pages_io(file_cache_ref *ref, off_t offset, const iovec *vecs, size_t count,
TRACE(("FILE VEC [%lu] length %Ld\n", fileVecIndex, fileLeft));
// process the complete fileVec
while (fileLeft > 0) {
iovec tempVecs[MAX_TEMP_IO_VECS];
uint32 tempCount = 1;
uint32 tempCount = 0;
size = min_c(vecs[i].iov_len - vecOffset, fileLeft);
// size tracks how much of what is left of the current fileVec
// (fileLeft) has been assigned to tempVecs
size = 0;
tempVecs[0].iov_base = (void *)((addr_t)vecs[i].iov_base + vecOffset);
tempVecs[0].iov_len = size;
if (size >= fileLeft)
vecOffset += size;
else
vecOffset = 0;
while (size < fileLeft && ++i < count
&& tempCount < MAX_TEMP_IO_VECS) {
// assign what is left of the current fileVec to the tempVecs
while (size < fileLeft && i < count
&& tempCount < MAX_TEMP_IO_VECS) {
// try to satisfy one iovec per iteration (or as much as
// possible)
TRACE(("fill vec %ld, offset = %lu, size = %lu\n",
i, vecOffset, size));
tempVecs[tempCount].iov_base = vecs[i].iov_base;
// is this iovec larger than the file_io_vec?
if (vecs[i].iov_len + size > fileLeft) {
size += tempVecs[tempCount].iov_len
= vecOffset = fileLeft - size;
tempCount++;
break;
// bytes left of the current iovec
size_t vecLeft = vecs[i].iov_len - vecOffset;
if (vecLeft == 0) {
i++;
vecOffset = 0;
continue;
}
size += tempVecs[tempCount].iov_len = vecs[i].iov_len;
// actually available bytes
size_t tempVecSize = min_c(vecLeft, fileLeft - size);
tempVecs[tempCount].iov_base
= (void *)((addr_t)vecs[i].iov_base + vecOffset);
tempVecs[tempCount].iov_len = tempVecSize;
tempCount++;
size += tempVecSize;
vecOffset += tempVecSize;
}
size_t bytes = size;
@ -459,20 +463,21 @@ pages_io(file_cache_ref *ref, off_t offset, const iovec *vecs, size_t count,
if (status < B_OK)
return status;
totalSize += size;
totalSize += bytes;
bytesLeft -= size;
fileOffset += size;
fileLeft -= size;
//dprintf("-> file left = %Lu\n", fileLeft);
if (size != bytes) {
// there are no more bytes, let's bail out
if (size != bytes || i >= count) {
// there are no more bytes or iovecs, let's bail out
*_numBytes = totalSize;
return B_OK;
}
}
}
*_numBytes = totalSize;
return B_OK;
}