diff options
Diffstat (limited to 'libstore/rdwr.c')
| -rw-r--r-- | libstore/rdwr.c | 285 |
1 files changed, 163 insertions, 122 deletions
diff --git a/libstore/rdwr.c b/libstore/rdwr.c index 020f4f2f..4266f715 100644 --- a/libstore/rdwr.c +++ b/libstore/rdwr.c @@ -20,165 +20,206 @@ with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ -/* Write LEN bytes from BUF to STORE at ADDR. If AMOUNT is NULL, returns EIO - if less than LEN bytes were written, otherwise returns the amount written +#include "store.h" + +/* Returns in RUNS the tail of STORE's run list, who's first run contains + ADDR, and is not a whole, and in RUNS_END a pointer pointing at the end of + the run list. Returns the offset within it at which ADDR occurs. */ +static inline off_t +store_find_first_run (struct store *store, off_t addr, + off_t **runs, unsigned *runs_end) +{ + off_t *tail = store->runs, *tail_end = tail + store->runs_len; + + /* XXX: this isn't going to be very efficient if RUNS is very complex... + But it should do dandy if it's short. For long run lists, we could do a + binary search or something. */ + while (tail < tail_end) + { + off_t run_addr = tail[0]; + off_t run_blocks = tail[1]; + + if (run_blocks > addr) + { + *runs = tail; + *runs_end = tail_end; + return addr; + } + + /* Not to the right place yet, move on... */ + addr -= run_blocks; + tail += 2; + } + + return -1; +} + +/* Write LEN bytes from BUF to STORE at ADDR. Returns the amount written in AMOUNT. ADDR is in BLOCKS (as defined by store->block_size). */ error_t store_write (struct store *store, off_t addr, char *buf, size_t len, size_t *amount); { - error_t err = EIO; /* What happens if we run off the end */ - size_t total_written = 0; - off_t *runs = store->runs; - unsigned runs_len = store->runs_len; + error_t err; + off_t *runs; + unsigned runs_end; store_write_meth_t write = store->meths->write; - int block_shift = store->log2_block_size; - /* XXX: this isn't going to be very efficient if RUNS is very complex... - But it should do dandy if it's short. For long run lists, we could do a - binary search or something to find the starting run. */ - while (runs_len) + addr = store_find_first_run (store, addr, &runs, &runs_end); + if (addr < 0) + err = EIO; + else if (runs[1] >= len) + /* The first run has it all... */ + err = (*write)(store, runs[0] + addr, buf, len, amount); + else + /* ARGH, we've got to split up the write ... */ { - off_t run_addr = runs[0]; - off_t run_blocks = runs[1]; - - if (run_blocks <= addr) - /* Not to the right place yet, move on... */ - addr -= run_blocks; - else if (run_addr < 0) - /* A hole! Can't write here. Must stop. If no data's been written - so far, ERR will still contain EIO, otherwise it will contain 0 - and we'll just return a short write. */ - break; - else - /* Ok, we can write in this run, at least a bit. */ - { - size_t written, blocks_written; - off_t run_len = (run_blocks << block_shift); - off_t end = (addr << block_shift) + len; - off_t seg_len = end > run_len ? run_len - addr : len; + off_t written; - /* Write to the actual object at the correct address. */ - err = (*write)(store, run_addr + addr, buf, seg_len, &written); - if (err) - /* Ack */ - break; + /* Write the initial bit in the first run. Errors here are returned. */ + err = (*write)(store, runs[0] + addr, buf, runs[1], &written); - total_written += written; + if (!err && written == runs[1]) + /* Wrote the first bit successfully, now do the rest. Any errors + will just result in a short write. */ + { + int block_shift = store->log2_block_size; + buf += written; len -= written; - if (len == 0) - break; /* All data written */ - buf += written; + runs += 2; + while (runs != runs_end) + { + off_t run_addr = runs[0]; + off_t run_blocks = runs[1]; - blocks_written = written >> block_shift; - if ((blocks_written << block_shift) != seg_amount) - /* A non-block multiple amount was written!? What do we do? */ - break; + if (run_addr < 0) + /* A hole! Can't write here. Must stop. */ + break; + else + /* Ok, we can write in this run, at least a bit. */ + { + off_t run_len = (run_blocks << block_shift); + off_t seg_len = run_len > len ? len : run_len; - addr += blocks_written; - } + err = (*write)(store, run_addr, buf, seg_len, &seg_written); + if (err) + break; /* Ack */ - runs += 2; - runs_len -= 2; - } + written += seg_written; + if (seg_written < run_len) + break; /* Didn't use up the run, we're done. */ - if (amount) - /* The user wants to know about short writes. */ - { - if (total_written) - err = 0; /* return a short write */ - *amount = total_written; + len -= seg_written; + if (len == 0) + break; /* Nothing left to write! */ + + buf += written; + } + + runs += 2; + } + } + + *amount = written; } - else if (!err) - /* Since there's no way to return the amount actually written, signal an - error. */ - err = EIO; return err; } - + error_t store_read (struct store *store, off_t addr, size_t amount, char **buf, size_t *len) { - error_t err = EIO; /* What happens if we run off the end */ - size_t total_read = 0; - off_t *runs = store->runs; - unsigned runs_len = store->runs_len; + error_t err; + off_t *runs; + unsigned runs_end; store_read_meth_t read = store->meths->read; - int block_shift = store->log2_block_size; - /* XXX: this isn't going to be very efficient if RUNS is very complex... - But it should do dandy if it's short. For long run lists, we could do a - binary search or something to find the starting run. */ - while (runs_len) + addr = store_find_first_run (store, addr, &runs, &runs_end); + if (addr < 0) + err = EIO; + else if (runs[1] >= len) + /* The first run has it all... */ + err = (*read)(store, runs[0] + addr, amount, buf, len); + else + /* ARGH, we've got to split up the write ... This isn't fun. */ { - off_t run_addr = runs[0]; - off_t run_blocks = runs[1]; - - if (run_blocks <= addr) - /* Not to the right place yet, move on... */ - addr -= run_blocks; - else if (run_addr < 0) - /* A hole! Can't read here. Must stop. If no data's been read - so far, ERR will still contain EIO, otherwise it will contain 0 - and we'll just return a short read. */ - break; - else - /* Ok, we can read in this run, at least a bit. */ + int all; + /* WHOLE_BUF and WHOLE_BUF_LEN will point to a buff that's large enough + to hold the entire request. This is initially whatever the user + passed in, but we'll change it as necessary. */ + char *whole_buf = *buf, *buf_end = whole_buf; + size_t whole_buf_len = *len, buf_left = whole_buf_len; + + /* Read LEN bytes from the store address ADDR into BUF_LEN. BUF_LEN + and AMOUNT are adjusted by the amount actually read. Whether or not + the amount read is the same as what was request is returned in ALL. */ + inline error_t seg_read (off_t addr, off_t len, int *all) { - size_t seg_read, blocks_read; - off_t run_len = (run_blocks << block_shift); - off_t end = (addr << block_shift) + amount; - off_t seg_amount = end > run_len ? run_len - addr : amount; - - /* Read to the actual object at the correct address. */ - if (total_read) - /* Some stuff has already been read, so we have to worry about - coalescing the return buffers. */ - { - - } - else + /* SEG_BUF and SEG_LEN are the buffer for a particular bit of the + whole (within one run). */ + char *seg_buf = buf_end; + size_t seg_buf_len = len; + error_t err = (*read)(store, addr, len, &seg_buf, &seg_buf_len); + if (!err) { - err = (*read)(store, run_addr + addr, seg_amount, buf, len); - if (err) - /* Ack */ - break; - seg_read = len; + /* If for some bizarre reason, the underlying storage chose not + to use the buffer space we so kindly gave it, bcopy it to + that space. */ + if (seg_buf != buf_end) + bcopy (seg_buf, buf_end, seg_buf_len); + buf_end += seg_buf_len; + amount -= seg_buf_len; + *all = (seg_buf_len == len); } + } - total_read += seg_read; + if (whole_buf_left < amount) + /* Not enough room in the user's buffer to hold everything, better + make room. */ + { + whole_buf_left = amount; + err = vm_allocate (mach_task_self (), &whole_buf, amount, 1); + if (err) + return err; /* Punt early, there's nothing to clean up. */ + } - amount -= seg_read; - if (amount == 0) - break; /* All data read */ + err = seg_read (store, runs[0] + addr, runs[1], &all); - blocks_read = seg_read >> block_shift; - if ((blocks_read << block_shift) != seg_amount) - /* A non-block multiple amount was read!? What do we do? */ - break; + if (!err && all) + { + runs += 2; + while (!err && runs != runs_end && all) + { + off_t run_addr = runs[0]; + off_t run_blocks = runs[1]; - addr += blocks_read; + if (run_addr < 0) + /* A hole! Can't write here. Must stop. */ + break; + else if (amount == 0) + break; + else + { + off_t run_len = (run_blocks << block_shift); + off_t seg_len = run_len > amount ? amount : run_len; + err = seg_read (run_addr, seg_len, &all); + } + + runs +=2; + } } - runs += 2; - runs_len -= 2; - } + /* The actual amount written. */ + *len = whole_buf_len - amount; XXXXXXXXX - if (amount) - /* The user wants to know about short reads. */ - { - if (total_read) - err = 0; /* return a short read!! */ - *amount = total_read; + /* Deallocate any amount of WHOLE_BUF we didn't use. */ + if (whole_buf != *buf) + { + *buf = whole_buf; + } } - else if (!err) - /* Since there's no way to return the amount actually read, signal an - error. */ - err = EIO; - - return err; } + |