drivers/staging/android/logger.c

   1 /*
   2  * drivers/misc/logger.c
   3  *
   4  * A Logging Subsystem
   5  *
   6  * Copyright (C) 2007-2008 Google, Inc.
   7  *
   8  * Robert Love <rlove@google.com>
   9  *
  10  * This software is licensed under the terms of the GNU General Public
  11  * License version 2, as published by the Free Software Foundation, and
  12  * may be copied, distributed, and modified under those terms.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  */
  19
  20 #define pr_fmt(fmt) "logger: " fmt
  21
  22 #include <linux/sched/signal.h>
  23 #include <linux/module.h>
  24 #include <linux/fs.h>
  25 #include <linux/miscdevice.h>
  26 #include <linux/uaccess.h>
  27 #include <linux/poll.h>
  28 #include <linux/slab.h>
  29 #include <linux/time.h>
  30 #include <linux/vmalloc.h>
  31 #include <linux/uio.h>
  32 #include <linux/fdtable.h>
  33 #include <linux/file.h>
  34
  35 #include "logger.h"
  36
  37 /**
  38  * struct logger_log - represents a specific log, such as 'main' or 'radio'
  39  * @buffer:     The actual ring buffer
  40  * @misc:       The "misc" device representing the log
  41  * @wq:         The wait queue for @readers
  42  * @readers:    This log's readers
  43  * @mutex:      The mutex that protects the @buffer
  44  * @w_off:      The current write head offset
  45  * @head:       The head, or location that readers start reading at.
  46  * @size:       The size of the log
  47  * @logs:       The list of log channels
  48  *
  49  * This structure lives from module insertion until module removal, so it does
  50  * not need additional reference counting. The structure is protected by the
  51  * mutex 'mutex'.
  52  */
  53 struct logger_log {
  54         unsigned char           *buffer;
  55         struct miscdevice       misc;
  56         wait_queue_head_t       wq;
  57         struct list_head        readers;
  58         struct mutex            mutex;
  59         size_t                  w_off;
  60         size_t                  head;
  61         size_t                  size;
  62         struct list_head        logs;
  63 };
  64
  65 static LIST_HEAD(log_list);
  66
  67 /**
  68  * struct log_writer - a logging device open for writing
  69  * @log:        The associated log
  70  * @list:       The associated entry in @logger_log's list
  71  * @b_off:      The current position in @buf
  72  * @tag:        A tag to be attached to messages
  73  * @prio:       Default message priority value
  74  * @buff:       Temporary space to assemble messages.
  75  */
  76 struct logger_writer {
  77         struct logger_log       *log;
  78         struct task_struct      *owner;
  79         struct task_struct      *b_owner;
  80         struct logger_entry     b_header;
  81         size_t                  b_off;
  82         size_t                  tag_len;
  83         char                    *tag;
  84         int                     prio;
  85         char                    *buffer;
  86 };
  87
  88 /**
  89  * struct logger_reader - a logging device open for reading
  90  * @log:        The associated log
  91  * @list:       The associated entry in @logger_log's list
  92  * @r_off:      The current read head offset.
  93  * @r_all:      Reader can read all entries
  94  * @r_ver:      Reader ABI version
  95  *
  96  * This object lives from open to release, so we don't need additional
  97  * reference counting. The structure is protected by log->mutex.
  98  */
  99 struct logger_reader {
 100         struct logger_log       *log;
 101         struct list_head        list;
 102         size_t                  r_off;
 103         bool                    r_all;
 104         int                     r_ver;
 105 };
 106
 107 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
 108 static size_t logger_offset(struct logger_log *log, size_t n)
 109 {
 110         return n & (log->size - 1);
 111 }
 112
 113 /*
 114  * file_get_log - Given a file structure, return the associated log
 115  *
 116  * This isn't aesthetic. We have several goals:
 117  *
 118  *      1) Need to quickly obtain the associated log during an I/O operation
 119  *      2) Readers need to maintain state (logger_reader)
 120  *      3) Writers need to be very fast (open() should be a near no-op)
 121  *
 122  * In the reader case, we can trivially go file->logger_reader->logger_log.
 123  * For a writer, we don't want to maintain a logger_reader, so we just go
 124  * file->logger_log. Thus what file->private_data points at depends on whether
 125  * or not the file was opened for reading. This function hides that dirtiness.
 126  */
 127 static inline struct logger_log *file_get_log(struct file *file)
 128 {
 129         struct logger_writer *writer = file->private_data;
 130
 131         if (file->f_mode & FMODE_READ) {
 132                 struct logger_reader *reader = file->private_data;
 133
 134                 return reader->log;
 135         }
 136
 137         return writer->log;
 138 }
 139
 140 /*
 141  * get_entry_header - returns a pointer to the logger_entry header within
 142  * 'log' starting at offset 'off'. A temporary logger_entry 'scratch' must
 143  * be provided. Typically the return value will be a pointer within
 144  * 'logger->buf'.  However, a pointer to 'scratch' may be returned if
 145  * the log entry spans the end and beginning of the circular buffer.
 146  */
 147 static struct logger_entry *get_entry_header(struct logger_log *log,
 148                                              size_t off,
 149                                              struct logger_entry *scratch)
 150 {
 151         size_t len = min(sizeof(struct logger_entry), log->size - off);
 152
 153         if (len != sizeof(struct logger_entry)) {
 154                 memcpy(((void *)scratch), log->buffer + off, len);
 155                 memcpy(((void *)scratch) + len, log->buffer,
 156                        sizeof(struct logger_entry) - len);
 157                 return scratch;
 158         }
 159
 160         return (struct logger_entry *) (log->buffer + off);
 161 }
 162
 163 /*
 164  * get_entry_msg_len - Grabs the length of the message of the entry
 165  * starting from from 'off'.
 166  *
 167  * An entry length is 2 bytes (16 bits) in host endian order.
 168  * In the log, the length does not include the size of the log entry structure.
 169  * This function returns the size including the log entry structure.
 170  *
 171  * Caller needs to hold log->mutex.
 172  */
 173 static __u32 get_entry_msg_len(struct logger_log *log, size_t off)
 174 {
 175         struct logger_entry scratch;
 176         struct logger_entry *entry;
 177
 178         entry = get_entry_header(log, off, &scratch);
 179         return entry->len;
 180 }
 181
 182 static size_t get_user_hdr_len(int ver)
 183 {
 184         if (ver < 2)
 185                 return sizeof(struct user_logger_entry_compat);
 186         return sizeof(struct logger_entry);
 187 }
 188
 189 static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
 190                                    char __user *buf)
 191 {
 192         void *hdr;
 193         size_t hdr_len;
 194         struct user_logger_entry_compat v1;
 195
 196         if (ver < 2) {
 197                 v1.len      = entry->len;
 198                 v1.__pad    = 0;
 199                 v1.pid      = entry->pid;
 200                 v1.tid      = entry->tid;
 201                 v1.sec      = entry->sec;
 202                 v1.nsec     = entry->nsec;
 203                 hdr         = &v1;
 204                 hdr_len     = sizeof(struct user_logger_entry_compat);
 205         } else {
 206                 hdr         = entry;
 207                 hdr_len     = sizeof(struct logger_entry);
 208         }
 209
 210         return copy_to_user(buf, hdr, hdr_len);
 211 }
 212
 213 /*
 214  * do_read_log_to_user - reads exactly 'count' bytes from 'log' into the
 215  * user-space buffer 'buf'. Returns 'count' on success.
 216  *
 217  * Caller must hold log->mutex.
 218  */
 219 static ssize_t do_read_log_to_user(struct logger_log *log,
 220                                    struct logger_reader *reader,
 221                                    char __user *buf,
 222                                    size_t count)
 223 {
 224         struct logger_entry scratch;
 225         struct logger_entry *entry;
 226         size_t len;
 227         size_t msg_start;
 228
 229         /*
 230          * First, copy the header to userspace, using the version of
 231          * the header requested
 232          */
 233         entry = get_entry_header(log, reader->r_off, &scratch);
 234         if (copy_header_to_user(reader->r_ver, entry, buf))
 235                 return -EFAULT;
 236
 237         count -= get_user_hdr_len(reader->r_ver);
 238         buf += get_user_hdr_len(reader->r_ver);
 239         msg_start = logger_offset(log,
 240                                   reader->r_off + sizeof(struct logger_entry));
 241
 242         /*
 243          * We read from the msg in two disjoint operations. First, we read from
 244          * the current msg head offset up to 'count' bytes or to the end of
 245          * the log, whichever comes first.
 246          */
 247         len = min(count, log->size - msg_start);
 248         if (copy_to_user(buf, log->buffer + msg_start, len))
 249                 return -EFAULT;
 250
 251         /*
 252          * Second, we read any remaining bytes, starting back at the head of
 253          * the log.
 254          */
 255         if (count != len)
 256                 if (copy_to_user(buf + len, log->buffer, count - len))
 257                         return -EFAULT;
 258
 259         reader->r_off = logger_offset(log, reader->r_off +
 260                 sizeof(struct logger_entry) + count);
 261
 262         return count + get_user_hdr_len(reader->r_ver);
 263 }
 264
 265 /*
 266  * get_next_entry_by_uid - Starting at 'off', returns an offset into
 267  * 'log->buffer' which contains the first entry readable by 'euid'
 268  */
 269 static size_t get_next_entry_by_uid(struct logger_log *log,
 270                                     size_t off, kuid_t euid)
 271 {
 272         while (off != log->w_off) {
 273                 struct logger_entry *entry;
 274                 struct logger_entry scratch;
 275                 size_t next_len;
 276
 277                 entry = get_entry_header(log, off, &scratch);
 278
 279                 if (uid_eq(entry->euid, euid))
 280                         return off;
 281
 282                 next_len = sizeof(struct logger_entry) + entry->len;
 283                 off = logger_offset(log, off + next_len);
 284         }
 285
 286         return off;
 287 }
 288
 289 /*
 290  * logger_read - our log's read() method
 291  *
 292  * Behavior:
 293  *
 294  *      - O_NONBLOCK works
 295  *      - If there are no log entries to read, blocks until log is written to
 296  *      - Atomically reads exactly one log entry
 297  *
 298  * Will set errno to EINVAL if read
 299  * buffer is insufficient to hold next entry.
 300  */
 301 static ssize_t logger_read(struct file *file, char __user *buf,
 302                            size_t count, loff_t *pos)
 303 {
 304         struct logger_reader *reader = file->private_data;
 305         struct logger_log *log = reader->log;
 306         ssize_t ret;
 307         DEFINE_WAIT(wait);
 308
 309 start:
 310         while (1) {
 311                 mutex_lock(&log->mutex);
 312
 313                 prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
 314
 315                 ret = (log->w_off == reader->r_off);
 316                 mutex_unlock(&log->mutex);
 317                 if (!ret)
 318                         break;
 319
 320                 if (file->f_flags & O_NONBLOCK) {
 321                         ret = -EAGAIN;
 322                         break;
 323                 }
 324
 325                 if (signal_pending(current)) {
 326                         ret = -EINTR;
 327                         break;
 328                 }
 329
 330                 schedule();
 331         }
 332
 333         finish_wait(&log->wq, &wait);
 334         if (ret)
 335                 return ret;
 336
 337         mutex_lock(&log->mutex);
 338
 339         if (!reader->r_all)
 340                 reader->r_off = get_next_entry_by_uid(log,
 341                         reader->r_off, current_euid());
 342
 343         /* is there still something to read or did we race? */
 344         if (unlikely(log->w_off == reader->r_off)) {
 345                 mutex_unlock(&log->mutex);
 346                 goto start;
 347         }
 348
 349         /* get the size of the next entry */
 350         ret = get_user_hdr_len(reader->r_ver) +
 351                 get_entry_msg_len(log, reader->r_off);
 352         if (count < ret) {
 353                 ret = -EINVAL;
 354                 goto out;
 355         }
 356
 357         /* get exactly one entry from the log */
 358         ret = do_read_log_to_user(log, reader, buf, ret);
 359
 360 out:
 361         mutex_unlock(&log->mutex);
 362
 363         return ret;
 364 }
 365
 366 /*
 367  * get_next_entry - return the offset of the first valid entry at least 'len'
 368  * bytes after 'off'.
 369  *
 370  * Caller must hold log->mutex.
 371  */
 372 static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
 373 {
 374         size_t count = 0;
 375
 376         do {
 377                 size_t nr = sizeof(struct logger_entry) +
 378                         get_entry_msg_len(log, off);
 379                 off = logger_offset(log, off + nr);
 380                 count += nr;
 381         } while (count < len);
 382
 383         return off;
 384 }
 385
 386 /*
 387  * is_between - is a < c < b, accounting for wrapping of a, b, and c
 388  *    positions in the buffer
 389  *
 390  * That is, if a<b, check for c between a and b
 391  * and if a>b, check for c outside (not between) a and b
 392  *
 393  * |------- a xxxxxxxx b --------|
 394  *               c^
 395  *
 396  * |xxxxx b --------- a xxxxxxxxx|
 397  *    c^
 398  *  or                    c^
 399  */
 400 static inline int is_between(size_t a, size_t b, size_t c)
 401 {
 402         if (a < b) {
 403                 /* is c between a and b? */
 404                 if (a < c && c <= b)
 405                         return 1;
 406         } else {
 407                 /* is c outside of b through a? */
 408                 if (c <= b || a < c)
 409                         return 1;
 410         }
 411
 412         return 0;
 413 }
 414
 415 /*
 416  * fix_up_readers - walk the list of all readers and "fix up" any who were
 417  * lapped by the writer; also do the same for the default "start head".
 418  * We do this by "pulling forward" the readers and start head to the first
 419  * entry after the new write head.
 420  *
 421  * The caller needs to hold log->mutex.
 422  */
 423 static void fix_up_readers(struct logger_log *log, size_t len)
 424 {
 425         size_t old = log->w_off;
 426         size_t new = logger_offset(log, old + len);
 427         struct logger_reader *reader;
 428
 429         if (is_between(old, new, log->head))
 430                 log->head = get_next_entry(log, log->head, len);
 431
 432         list_for_each_entry(reader, &log->readers, list)
 433                 if (is_between(old, new, reader->r_off))
 434                         reader->r_off = get_next_entry(log, reader->r_off, len);
 435 }
 436
 437 static char *strnrchr(const char *s, size_t count, int c)
 438 {
 439         const char *last = NULL;
 440         if (!count)
 441                 return NULL;
 442         do {
 443                 if (*s == (char)c)
 444                         last = s;
 445         } while (--count && *s++);
 446         return (char *)last;
 447 }
 448
 449 static struct file *replace_file(struct files_struct *files,
 450                                  struct file *oldf,
 451                                  struct file *newf)
 452 {
 453         struct file *file = NULL;
 454         struct fdtable *fdt;
 455         unsigned int i;
 456
 457         spin_lock(&files->file_lock);
 458         fdt = files_fdtable(files);
 459         for (i = 0; i < fdt->max_fds && file != oldf; i++) {
 460                 if (fdt->fd[i] == oldf) {
 461                         file = xchg(&fdt->fd[i], newf);
 462                 }
 463         }
 464         spin_unlock(&files->file_lock);
 465
 466         if (file)
 467                 filp_close(file, files);
 468
 469         return file;
 470 }
 471
 472 static struct file *make_new_file(struct file *file)
 473 {
 474         struct logger_writer *writer = file->private_data;
 475         struct logger_writer *nwriter;
 476         struct file *nfile;
 477         char *pbuf, *p;
 478
 479         pbuf = kzalloc(PATH_MAX, GFP_KERNEL);
 480         if (!pbuf) {
 481                 return ERR_PTR(-ENOMEM);
 482         }
 483
 484         p = file_path(file, pbuf, PATH_MAX);
 485         if (!p) {
 486                 kfree(pbuf);
 487                 return ERR_PTR(-EFAULT);
 488         }
 489
 490         nfile = filp_open(p, O_WRONLY, 0);
 491         kfree(pbuf);
 492         if (!nfile) {
 493                 return ERR_PTR(-EFAULT);
 494         }
 495
 496         nwriter = nfile->private_data;
 497         nwriter->prio = writer->prio;
 498         nwriter->tag = kstrdup(writer->tag, GFP_KERNEL);
 499         nwriter->tag_len = writer->tag_len;
 500
 501         if (!replace_file(current->files, file, nfile)) {
 502                 filp_close(nfile, current->files);
 503                 return ERR_PTR(-EFAULT);
 504         }
 505
 506         return nfile;
 507 }
 508
 509 static void write_log_data(struct logger_log *log,
 510                            struct logger_entry *header,
 511                            struct logger_writer *writer,
 512                            size_t chunk_len)
 513 {
 514         size_t len, w_off;
 515
 516         /* header */
 517         len = min(sizeof(struct logger_entry), log->size - log->w_off);
 518         memcpy(log->buffer + log->w_off, header, len);
 519         memcpy(log->buffer, (char *)header + len, sizeof(struct logger_entry) - len);
 520         w_off =  logger_offset(log, log->w_off + sizeof(struct logger_entry));
 521
 522         /* priority */
 523         log->buffer[w_off] = (unsigned char)writer->prio;
 524         w_off = logger_offset(log, w_off + 1);
 525
 526         /* tag */
 527         len = min_t(size_t, writer->tag_len + 1, log->size - w_off);
 528         memcpy(log->buffer + w_off, writer->tag, len);
 529         memcpy(log->buffer, writer->tag + len, writer->tag_len + 1 - len);
 530         w_off = logger_offset(log, w_off + writer->tag_len + 1);
 531
 532         /* message */
 533         len = min(chunk_len, log->size - w_off);
 534         memcpy(log->buffer + w_off, writer->buffer, len);
 535         memcpy(log->buffer, writer->buffer + len, chunk_len - len);
 536         log->w_off = logger_offset(log, w_off + chunk_len);
 537 }
 538
 539 static void flush_thread_data(struct file* file)
 540 {
 541         struct logger_writer *writer = file->private_data;
 542         struct logger_log *log = file_get_log(file);
 543         size_t chunk_len = 0;
 544
 545         chunk_len = writer->b_off + 1;
 546         writer->b_header.len = chunk_len + writer->tag_len + 2;
 547
 548         fix_up_readers(log, sizeof(struct logger_entry) + writer->b_header.len);
 549
 550         write_log_data(log, &writer->b_header, writer, chunk_len);
 551
 552         writer->b_off = 0;
 553         writer->buffer[0] = '\0';
 554 }
 555
 556 /*
 557  * logger_write_iter - our write method, implementing support for write(),
 558  * writev(), and aio_write(). Writes are our fast path, and we try to optimize
 559  * them above all else.
 560  */
 561 static ssize_t logger_write_iter(struct kiocb *iocb, struct iov_iter *from)
 562 {
 563         struct file *file = iocb->ki_filp;
 564         struct logger_writer *writer = file->private_data;
 565         struct logger_log *log = file_get_log(file);
 566         struct logger_entry header;
 567         struct timespec64 now;
 568         size_t len, count, w_off;
 569         bool from_stdio = false;
 570
 571         if (writer->tag && writer->prio >= 2)
 572                 from_stdio = true;
 573
 574         count = min_t(size_t, iov_iter_count(from), LOGGER_ENTRY_MAX_PAYLOAD);
 575
 576         ktime_get_ts64(&now);
 577
 578         header.pid = current->tgid;
 579         header.tid = current->pid;
 580         header.sec = now.tv_sec;
 581         header.nsec = now.tv_nsec;
 582         header.euid = current_euid();
 583         header.len = count;
 584         header.hdr_size = sizeof(struct logger_entry);
 585
 586         /* null writes succeed, return zero */
 587         if (unlikely(!header.len))
 588                 return 0;
 589
 590         mutex_lock(&log->mutex);
 591
 592         /* Prepend messages from STDOUT and STDERR with a tag and prio */
 593         if (from_stdio) {
 594                 char *p;
 595                 size_t chunk_len = 0;
 596                 size_t max_payload = LOGGER_ENTRY_MAX_PAYLOAD - writer->tag_len - 2;
 597
 598                 if (writer->owner != current->group_leader) {
 599                         struct file *nfile;
 600
 601                         nfile = make_new_file(file);
 602                         if (IS_ERR(nfile)) {
 603                                 mutex_unlock(&log->mutex);
 604                                 return PTR_ERR(nfile);
 605                         }
 606
 607                         file = nfile;
 608                         writer = file->private_data;
 609                 }
 610
 611                 /* Allocate STDIO line buffer */
 612                 if (!writer->buffer) {
 613                         writer->buffer = kzalloc(LOGGER_ENTRY_MAX_PAYLOAD, GFP_KERNEL);
 614                         writer->b_off = 0;
 615
 616                         if (!writer->buffer) {
 617                                 mutex_unlock(&log->mutex);
 618                                 return -ENOMEM;
 619                         }
 620                 }
 621
 622                 /* flush message from a different thread */
 623                 if (writer->b_owner != current && writer->b_off)
 624                         flush_thread_data(file);
 625
 626                 count = min_t(size_t, iov_iter_count(from), max_payload - 1);
 627
 628                 do {
 629
 630                         if (copy_from_iter(writer->buffer + writer->b_off, count, from) != count) {
 631                                 mutex_unlock(&log->mutex);
 632                                 return -EFAULT;
 633                         }
 634
 635                         /* TODO: replace NULL characters with new lines */
 636                         p = strnrchr(writer->buffer + writer->b_off, count, '\n');
 637                         if (p) {
 638                                 *p++ = '\0';
 639                                 chunk_len = p - writer->buffer;
 640                         } else {
 641                                 writer->buffer[count++] = '\0';
 642                                 chunk_len = count;
 643                         }
 644
 645                         header.len = chunk_len + writer->tag_len + 2;
 646                         fix_up_readers(log, sizeof(struct logger_entry) + header.len);
 647
 648                         write_log_data(log, &header, writer, chunk_len);
 649
 650                         /* move the remaining part of the message */
 651                         memmove(writer->buffer, p, writer->b_off + count - chunk_len);
 652
 653                         /* new b_off points where the rimainder of the string ends */
 654                         writer->b_off = writer->b_off + count - chunk_len;
 655                         writer->buffer[writer->b_off] = '\0';
 656
 657                 } while ((count = min_t(size_t, iov_iter_count(from), max_payload - 1)));
 658
 659                 /* save for remaining unfinished line */
 660                 writer->b_header = header;
 661                 writer->b_owner = current;
 662         } else {
 663
 664                 /*
 665                  * Fix up any readers, pulling them forward to the first readable
 666                  * entry after (what will be) the new write offset. We do this now
 667                  * because if we partially fail, we can end up with clobbered log
 668                  * entries that encroach on readable buffer.
 669                  */
 670                 fix_up_readers(log, sizeof(struct logger_entry) + header.len);
 671
 672                 len = min(sizeof(header), log->size - log->w_off);
 673                 memcpy(log->buffer + log->w_off, &header, len);
 674                 memcpy(log->buffer, (char *)&header + len, sizeof(header) - len);
 675
 676                 /* Work with a copy until we are ready to commit the whole entry */
 677                 w_off =  logger_offset(log, log->w_off + sizeof(struct logger_entry));
 678
 679                 len = min(count, log->size - w_off);
 680
 681                 if (copy_from_iter(log->buffer + w_off, len, from) != len) {
 682                         /*
 683                          * Note that by not updating log->w_off, this abandons the
 684                          * portion of the new entry that *was* successfully
 685                          * copied, just above.  This is intentional to avoid
 686                          * message corruption from missing fragments.
 687                          */
 688                         mutex_unlock(&log->mutex);
 689                         return -EFAULT;
 690                 }
 691
 692                 if (copy_from_iter(log->buffer, count - len, from) != count - len) {
 693                         mutex_unlock(&log->mutex);
 694                         return -EFAULT;
 695                 }
 696
 697                 log->w_off = logger_offset(log, w_off + count);
 698         }
 699
 700         mutex_unlock(&log->mutex);
 701
 702         /* wake up any blocked readers */
 703         wake_up_interruptible(&log->wq);
 704
 705         return count;
 706 }
 707
 708 static struct logger_log *get_log_from_minor(int minor)
 709 {
 710         struct logger_log *log;
 711
 712         list_for_each_entry(log, &log_list, logs)
 713                 if (log->misc.minor == minor)
 714                         return log;
 715         return NULL;
 716 }
 717
 718 /*
 719  * logger_open - the log's open() file operation
 720  *
 721  * Note how near a no-op this is in the write-only case. Keep it that way!
 722  */
 723 static int logger_open(struct inode *inode, struct file *file)
 724 {
 725         struct logger_log *log;
 726         int ret;
 727
 728         ret = nonseekable_open(inode, file);
 729         if (ret)
 730                 return ret;
 731
 732         log = get_log_from_minor(MINOR(inode->i_rdev));
 733         if (!log)
 734                 return -ENODEV;
 735
 736         if (file->f_mode & FMODE_READ) {
 737                 struct logger_reader *reader;
 738
 739                 reader = kmalloc(sizeof(struct logger_reader), GFP_KERNEL);
 740                 if (!reader)
 741                         return -ENOMEM;
 742
 743                 reader->log = log;
 744                 reader->r_ver = 1;
 745                 reader->r_all = in_egroup_p(inode->i_gid) ||
 746                         capable(CAP_SYSLOG);
 747
 748                 INIT_LIST_HEAD(&reader->list);
 749
 750                 mutex_lock(&log->mutex);
 751                 reader->r_off = log->head;
 752                 list_add_tail(&reader->list, &log->readers);
 753                 mutex_unlock(&log->mutex);
 754
 755                 file->private_data = reader;
 756         } else {
 757                 struct logger_writer *writer;
 758
 759                 writer = kzalloc(sizeof(struct logger_writer), GFP_KERNEL);
 760                 if (!writer)
 761                         return -ENOMEM;
 762
 763                 writer->log = log;
 764                 writer->owner = current->group_leader;
 765
 766                 file->private_data = writer;
 767         }
 768
 769         return 0;
 770 }
 771
 772 /*
 773  * logger_release - the log's release file operation
 774  *
 775  * Note this is a total no-op in the write-only case. Keep it that way!
 776  */
 777 static int logger_release(struct inode *ignored, struct file *file)
 778 {
 779         if (file->f_mode & FMODE_READ) {
 780                 struct logger_reader *reader = file->private_data;
 781                 struct logger_log *log = reader->log;
 782
 783                 mutex_lock(&log->mutex);
 784                 list_del(&reader->list);
 785                 mutex_unlock(&log->mutex);
 786
 787                 kfree(reader);
 788         } else {
 789                 struct logger_writer *writer = file->private_data;
 790
 791                 kfree(writer->tag);
 792                 kfree(writer->buffer);
 793                 kfree(writer);
 794         }
 795
 796         return 0;
 797 }
 798
 799 /*
 800  * logger_poll - the log's poll file operation, for poll/select/epoll
 801  *
 802  * Note we always return POLLOUT, because you can always write() to the log.
 803  * Note also that, strictly speaking, a return value of POLLIN does not
 804  * guarantee that the log is readable without blocking, as there is a small
 805  * chance that the writer can lap the reader in the interim between poll()
 806  * returning and the read() request.
 807  */
 808 static unsigned int logger_poll(struct file *file, poll_table *wait)
 809 {
 810         struct logger_reader *reader;
 811         struct logger_log *log;
 812         unsigned int ret = POLLOUT | POLLWRNORM;
 813
 814         if (!(file->f_mode & FMODE_READ))
 815                 return ret;
 816
 817         reader = file->private_data;
 818         log = reader->log;
 819
 820         poll_wait(file, &log->wq, wait);
 821
 822         mutex_lock(&log->mutex);
 823         if (!reader->r_all)
 824                 reader->r_off = get_next_entry_by_uid(log,
 825                         reader->r_off, current_euid());
 826
 827         if (log->w_off != reader->r_off)
 828                 ret |= POLLIN | POLLRDNORM;
 829         mutex_unlock(&log->mutex);
 830
 831         return ret;
 832 }
 833
 834 static long logger_set_version(struct logger_reader *reader, void __user *arg)
 835 {
 836         int version;
 837
 838         if (copy_from_user(&version, arg, sizeof(int)))
 839                 return -EFAULT;
 840
 841         if ((version < 1) || (version > 2))
 842                 return -EINVAL;
 843
 844         reader->r_ver = version;
 845         return 0;
 846 }
 847
 848 static long logger_set_prio(struct logger_writer *writer, void __user *arg)
 849 {
 850         int prio;
 851
 852         prio = (int)(uintptr_t)arg;
 853
 854         if ((prio < 2) || (prio > 7))
 855                 return -EINVAL;
 856
 857         writer->prio = prio;
 858         return 0;
 859 }
 860
 861 static long logger_set_tag(struct logger_writer *writer, void __user *arg)
 862 {
 863         int len;
 864         char *p, *q;
 865
 866         if (copy_from_user(&len, arg, sizeof(int)))
 867                 return -EFAULT;
 868
 869         arg += sizeof(int);
 870
 871
 872         p = kzalloc(len, GFP_KERNEL);
 873         if (!p)
 874                 return -ENOMEM;
 875
 876         if (copy_from_user(p, arg, len)) {
 877                 kfree(p);
 878                 return -EFAULT;
 879         }
 880         p[len-1] = '\0';
 881
 882         q = writer->tag;
 883         writer->tag = p;
 884         writer->tag_len = len - 1; /* without NULL */
 885         kfree(q);
 886
 887         return 0;
 888 }
 889
 890 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 891 {
 892         struct logger_log *log = file_get_log(file);
 893         struct logger_reader *reader;
 894         struct logger_writer *writer;
 895         long ret = -EINVAL;
 896         void __user *argp = (void __user *)arg;
 897
 898         mutex_lock(&log->mutex);
 899
 900         switch (cmd) {
 901         case LOGGER_GET_LOG_BUF_SIZE:
 902                 ret = log->size;
 903                 break;
 904         case LOGGER_GET_LOG_LEN:
 905                 if (!(file->f_mode & FMODE_READ)) {
 906                         ret = -EBADF;
 907                         break;
 908                 }
 909                 reader = file->private_data;
 910                 if (log->w_off >= reader->r_off)
 911                         ret = log->w_off - reader->r_off;
 912                 else
 913                         ret = (log->size - reader->r_off) + log->w_off;
 914                 break;
 915         case LOGGER_GET_NEXT_ENTRY_LEN:
 916                 if (!(file->f_mode & FMODE_READ)) {
 917                         ret = -EBADF;
 918                         break;
 919                 }
 920                 reader = file->private_data;
 921
 922                 if (!reader->r_all)
 923                         reader->r_off = get_next_entry_by_uid(log,
 924                                 reader->r_off, current_euid());
 925
 926                 if (log->w_off != reader->r_off)
 927                         ret = get_user_hdr_len(reader->r_ver) +
 928                                 get_entry_msg_len(log, reader->r_off);
 929                 else
 930                         ret = 0;
 931                 break;
 932         case LOGGER_FLUSH_LOG:
 933                 if (!(in_egroup_p(file_inode(file)->i_gid) ||
 934                       capable(CAP_SYSLOG))) {
 935                         ret = -EPERM;
 936                         break;
 937                 }
 938                 list_for_each_entry(reader, &log->readers, list)
 939                         reader->r_off = log->w_off;
 940                 log->head = log->w_off;
 941                 ret = 0;
 942                 break;
 943         case LOGGER_GET_VERSION:
 944                 if (!(file->f_mode & FMODE_READ)) {
 945                         ret = -EBADF;
 946                         break;
 947                 }
 948                 reader = file->private_data;
 949                 ret = reader->r_ver;
 950                 break;
 951         case LOGGER_SET_VERSION:
 952                 if (!(file->f_mode & FMODE_READ)) {
 953                         ret = -EBADF;
 954                         break;
 955                 }
 956                 reader = file->private_data;
 957                 ret = logger_set_version(reader, argp);
 958                 break;
 959         case LOGGER_SET_PRIO:   /* 44552 */
 960                 if (file->f_mode & FMODE_READ) {
 961                         ret = -EBADF;
 962                         break;
 963                 }
 964                 writer = file->private_data;
 965                 ret = logger_set_prio(writer, argp);
 966                 break;
 967         case LOGGER_SET_TAG:    /* 44551 */
 968                 if (file->f_mode & FMODE_READ) {
 969                         ret = -EBADF;
 970                         break;
 971                 }
 972                 writer = file->private_data;
 973                 ret = logger_set_tag(writer, argp);
 974                 break;
 975         }
 976
 977         mutex_unlock(&log->mutex);
 978
 979         return ret;
 980 }
 981
 982 static const struct file_operations logger_fops = {
 983         .owner = THIS_MODULE,
 984         .read = logger_read,
 985         .write_iter = logger_write_iter,
 986         .poll = logger_poll,
 987         .unlocked_ioctl = logger_ioctl,
 988         .compat_ioctl = logger_ioctl,
 989         .open = logger_open,
 990         .release = logger_release,
 991 };
 992
 993 /*
 994  * Log size must must be a power of two, and greater than
 995  * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
 996  */
 997 static int __init create_log(char *log_name, int size)
 998 {
 999         int ret = 0;
1000         struct logger_log *log;
1001         unsigned char *buffer;
1002
1003         buffer = vmalloc(size);
1004         if (buffer == NULL)
1005                 return -ENOMEM;
1006
1007         log = kzalloc(sizeof(struct logger_log), GFP_KERNEL);
1008         if (log == NULL) {
1009                 ret = -ENOMEM;
1010                 goto out_free_buffer;
1011         }
1012         log->buffer = buffer;
1013
1014         log->misc.minor = MISC_DYNAMIC_MINOR;
1015         log->misc.name = kstrdup(log_name, GFP_KERNEL);
1016         if (log->misc.name == NULL) {
1017                 ret = -ENOMEM;
1018                 goto out_free_log;
1019         }
1020
1021         log->misc.fops = &logger_fops;
1022         log->misc.parent = NULL;
1023
1024         init_waitqueue_head(&log->wq);
1025         INIT_LIST_HEAD(&log->readers);
1026         mutex_init(&log->mutex);
1027         log->w_off = 0;
1028         log->head = 0;
1029         log->size = size;
1030
1031         INIT_LIST_HEAD(&log->logs);
1032         list_add_tail(&log->logs, &log_list);
1033
1034         /* finally, initialize the misc device for this log */
1035         ret = misc_register(&log->misc);
1036         if (unlikely(ret)) {
1037                 pr_err("failed to register misc device for log '%s'!\n",
1038                        log->misc.name);
1039                 goto out_free_misc_name;
1040         }
1041
1042         pr_info("created %luK log '%s'\n",
1043                 (unsigned long)log->size >> 10, log->misc.name);
1044
1045         return 0;
1046
1047 out_free_misc_name:
1048         kfree(log->misc.name);
1049
1050 out_free_log:
1051         kfree(log);
1052
1053 out_free_buffer:
1054         vfree(buffer);
1055         return ret;
1056 }
1057
1058 static int __init logger_init(void)
1059 {
1060         int ret;
1061
1062         ret = create_log(LOGGER_LOG_MAIN, 256*1024);
1063         if (unlikely(ret))
1064                 goto out;
1065
1066         ret = create_log(LOGGER_LOG_EVENTS, 256*1024);
1067         if (unlikely(ret))
1068                 goto out;
1069
1070         ret = create_log(LOGGER_LOG_RADIO, 256*1024);
1071         if (unlikely(ret))
1072                 goto out;
1073
1074         ret = create_log(LOGGER_LOG_SYSTEM, 256*1024);
1075         if (unlikely(ret))
1076                 goto out;
1077
1078 out:
1079         return ret;
1080 }
1081
1082 static void __exit logger_exit(void)
1083 {
1084         struct logger_log *current_log, *next_log;
1085
1086         list_for_each_entry_safe(current_log, next_log, &log_list, logs) {
1087                 /* we have to delete all the entry inside log_list */
1088                 misc_deregister(&current_log->misc);
1089                 vfree(current_log->buffer);
1090                 kfree(current_log->misc.name);
1091                 list_del(&current_log->logs);
1092                 kfree(current_log);
1093         }
1094 }
1095
1096 device_initcall(logger_init);
1097 module_exit(logger_exit);
1098
1099 MODULE_LICENSE("GPL");
1100 MODULE_AUTHOR("Robert Love, <rlove@google.com>");
1101 MODULE_DESCRIPTION("Android Logger");