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https://issues.apache.org/jira/browse/HADOOP-3784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12635914#action_12635914
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Pete Wyckoff commented on HADOOP-3784:
--------------------------------------
correct implementation of reads
{code}
/**
* dfs_read
*
* Reads from dfs or the open file's buffer. Note that fuse requires that
* either the entire read be satisfied or the EOF is hit or direct_io is
enabled
*
*/
static int dfs_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
// retrieve dfs specific data
dfs_context *dfs = (dfs_context*)fuse_get_context()->private_data;
// check params and the context var
assert(dfs);
assert(path);
assert(buf);
assert(offset >= 0);
assert(size >= 0);
dfs_fh *fh = (dfs_fh*)fi->fh;
assert(fh->bufferSize >= 0);
// check if the buffer is empty or
// the read starts before the buffer starts or
// the read ends after the buffer ends
if (fh->bufferSize == 0 ||
offset < fh->buffersStartOffset ||
offset + size > fh->buffersStartOffset + fh->bufferSize)
{
// Read into the buffer from DFS
size_t num_read = 0;
size_t total_read = 0;
// if the size is bigger than the read buffer, then use the passed in
buffer
const char *buf_ptr = size >= dfs->rdbuffer_size ? buf : fh->buf;
size_t cur_left = size >= dfs->rdbuffer_size ? size : dfs->rdbuffer_size;
while(cur_left > 0 && (num_read = hdfsPread(fh->fs, fh->hdfsFH, offset +
total_read, buf_ptr + total_read, cur_left)) > 0) {
cur_left -= num_read;
total_read += num_read;
}
if (num_read < 0) {
// invalidate the buffer
fh->bufferSize = 0;
syslog(LOG_ERR, "Read error - pread failed for %s with return code %d
%s:%d", path, (int)num_read, __FILE__, __LINE__);
return -EIO;
}
if(size >= dfs->rdbuffer_size) {
// we read into the passed in buffer, so no need to do anything else
return total_read;
}
fh->bufferSize = total_read;
fh->buffersStartOffset = offset;
}
assert(offset >= fh->buffersStartOffset);
const size_t bufferReadIndex = offset - fh->buffersStartOffset;
assert(bufferReadIndex >= 0 && bufferReadIndex < fh->bufferSize);
const size_t amount = min(fh->buffersStartOffset + fh->bufferSize - offset,
size);
assert(amount >= 0 && amount <= fh->bufferSize);
const char *offsetPtr = fh->buf + bufferReadIndex;
assert(offsetPtr >= fh->buf);
assert(offsetPtr + amount <= fh->buf + fh->bufferSize);
memcpy(buf, offsetPtr, amount);
return amount;
}
{code}
> Cleanup optimization of reads and change it to a flag and remove #ifdefs
> ------------------------------------------------------------------------
>
> Key: HADOOP-3784
> URL: https://issues.apache.org/jira/browse/HADOOP-3784
> Project: Hadoop Core
> Issue Type: Improvement
> Components: contrib/fuse-dfs
> Reporter: Pete Wyckoff
>
> Looks like optimized reads work so let's make them part of the regular core
> of code. But, should allow a flag and custom sized buffer.
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