int
DRead(struct dcache *adc, int page, struct DirBuffer *entry)
{
/* Read a page from the disk. */
struct buffer *tb, *tb2;
struct osi_file *tfile;
int code;
AFS_STATCNT(DRead);
memset(entry, 0, sizeof(struct DirBuffer));
ObtainWriteLock(&afs_bufferLock, 256);
#define bufmatch(tb) (tb->page == page && tb->fid == adc->index)
#define buf_Front(head,parent,p) {(parent)->hashNext = (p)->hashNext; (p)->hashNext= *(head);*(head)=(p);}
/* this apparently-complicated-looking code is simply an example of
* a little bit of loop unrolling, and is a standard linked-list
* traversal trick. It saves a few assignments at the the expense
* of larger code size. This could be simplified by better use of
* macros.
*/
if ((tb = phTable[pHash(adc->index, page)])) {
if (bufmatch(tb)) {
ObtainWriteLock(&tb->lock, 257);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb->accesstime = timecounter++;
AFS_STATS(afs_stats_cmperf.bufHits++);
ReleaseWriteLock(&tb->lock);
entry->buffer = tb;
entry->data = tb->data;
return 0;
} else {
struct buffer **bufhead;
bufhead = &(phTable[pHash(adc->index, page)]);
while ((tb2 = tb->hashNext)) {
if (bufmatch(tb2)) {
buf_Front(bufhead, tb, tb2);
ObtainWriteLock(&tb2->lock, 258);
tb2->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb2->accesstime = timecounter++;
AFS_STATS(afs_stats_cmperf.bufHits++);
ReleaseWriteLock(&tb2->lock);
entry->buffer = tb2;
entry->data = tb2->data;
return 0;
}
if ((tb = tb2->hashNext)) {
if (bufmatch(tb)) {
buf_Front(bufhead, tb2, tb);
ObtainWriteLock(&tb->lock, 259);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb->accesstime = timecounter++;
AFS_STATS(afs_stats_cmperf.bufHits++);
ReleaseWriteLock(&tb->lock);
entry->buffer = tb;
entry->data = tb->data;
return 0;
}
} else
break;
}
}
} else
tb2 = NULL;
AFS_STATS(afs_stats_cmperf.bufMisses++);
/* can't find it */
/* The last thing we looked at was either tb or tb2 (or nothing). That
* is at least the oldest buffer on one particular hash chain, so it's
* a pretty good place to start looking for the truly oldest buffer.
*/
tb = afs_newslot(adc, page, (tb ? tb : tb2));
if (!tb) {
ReleaseWriteLock(&afs_bufferLock);
return EIO;
}
ObtainWriteLock(&tb->lock, 260);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
if (page * AFS_BUFFER_PAGESIZE >= adc->f.chunkBytes) {
tb->fid = NULLIDX;
afs_reset_inode(&tb->inode);
tb->lockers--;
ReleaseWriteLock(&tb->lock);
return EIO;
}
tfile = afs_CFileOpen(&adc->f.inode);
code =
afs_CFileRead(tfile, tb->page * AFS_BUFFER_PAGESIZE, tb->data,
AFS_BUFFER_PAGESIZE);
afs_CFileClose(tfile);
if (code < AFS_BUFFER_PAGESIZE) {
tb->fid = NULLIDX;
afs_reset_inode(&tb->inode);
tb->lockers--;
ReleaseWriteLock(&tb->lock);
return EIO;
}
/* Note that findslot sets the page field in the buffer equal to
* what it is searching for. */
ReleaseWriteLock(&tb->lock);
entry->buffer = tb;
entry->data = tb->data;
return 0;
}
/**
* read a page out of a directory object.
*
* @param[in] fid directory object fid
* @param[in] page page in hash table to be read
*
* @return pointer to requested page in directory cache
* @retval NULL read failed
*/
void *
DRead(afs_int32 *fid, int page)
{
/* Read a page from the disk. */
struct buffer *tb, *tb2, **bufhead;
ObtainWriteLock(&afs_bufferLock);
calls++;
#define bufmatch(tb) (tb->page == page && FidEq(tb->fid, fid))
#define buf_Front(head,parent,p) {(parent)->hashNext = (p)->hashNext; (p)->hashNext= *(head);*(head)=(p);}
/* this apparently-complicated-looking code is simply an example of
* a little bit of loop unrolling, and is a standard linked-list
* traversal trick. It saves a few assignments at the the expense
* of larger code size. This could be simplified by better use of
* macros. With the use of these LRU queues, the old one-cache is
* probably obsolete.
*/
if ((tb = phTable[pHash(fid)])) { /* ASSMT HERE */
if (bufmatch(tb)) {
ObtainWriteLock(&tb->lock);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb->accesstime = ++timecounter;
ReleaseWriteLock(&tb->lock);
return tb->data;
} else {
bufhead = &(phTable[pHash(fid)]);
while ((tb2 = tb->hashNext)) {
if (bufmatch(tb2)) {
buf_Front(bufhead, tb, tb2);
ObtainWriteLock(&tb2->lock);
tb2->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb2->accesstime = ++timecounter;
ReleaseWriteLock(&tb2->lock);
return tb2->data;
}
if ((tb = tb2->hashNext)) { /* ASSIGNMENT HERE! */
if (bufmatch(tb)) {
buf_Front(bufhead, tb2, tb);
ObtainWriteLock(&tb->lock);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
tb->accesstime = ++timecounter;
ReleaseWriteLock(&tb->lock);
return tb->data;
}
} else
break;
}
}
} else
tb2 = NULL;
/* can't find it */
/* The last thing we looked at was either tb or tb2 (or nothing). That
* is at least the oldest buffer on one particular hash chain, so it's
* a pretty good place to start looking for the truly oldest buffer.
*/
tb = newslot(fid, page, (tb ? tb : tb2));
ios++;
ObtainWriteLock(&tb->lock);
tb->lockers++;
ReleaseWriteLock(&afs_bufferLock);
if (ReallyRead(tb->fid, tb->page, tb->data)) {
tb->lockers--;
FidZap(tb->fid); /* disaster */
ReleaseWriteLock(&tb->lock);
return 0;
}
/* Note that findslot sets the page field in the buffer equal to
* what it is searching for.
*/
ReleaseWriteLock(&tb->lock);
return tb->data;
}