79b021d73
Denys Vlasenko
2009-08-10
Subject
tail: read only a portion of a file if it's huge. closes bug 551
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coreutils/tail.c+33 -16
| @@ -51,10 +51,10 @@ static ssize_t tail_read(int fd, char *buf, size_t count) | |
| struct stat sbuf; | |
| /* /proc files report zero st_size, don't lseek them. */ | |
| - | if (fstat(fd, &sbuf) == 0 && sbuf.st_size) { |
| + | if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) { |
| current = lseek(fd, 0, SEEK_CUR); | |
| if (sbuf.st_size < current) | |
| - | lseek(fd, 0, SEEK_SET); |
| + | xlseek(fd, 0, SEEK_SET); |
| } | |
| r = full_read(fd, buf, count); | |
| @@ -174,8 +174,9 @@ int tail_main(int argc, char **argv) | |
| int newlines_seen; | |
| unsigned seen; | |
| int nread; | |
| + | int fd = fds[i]; |
| - | if (ENABLE_FEATURE_FANCY_TAIL && fds[i] < 0) |
| + | if (ENABLE_FEATURE_FANCY_TAIL && fd < 0) |
| continue; /* may happen with -E */ | |
| if (nfiles > header_threshhold) { | |
| @@ -183,30 +184,46 @@ int tail_main(int argc, char **argv) | |
| fmt = header_fmt; | |
| } | |
| - | /* Optimizing count-bytes case if the file is seekable. |
| - | * Beware of backing up too far. |
| - | * Also we exclude files with size 0 (because of /proc/xxx) */ |
| - | if (COUNT_BYTES && !from_top) { |
| - | off_t current = lseek(fds[i], 0, SEEK_END); |
| + | if (!from_top) { |
| + | off_t current = lseek(fd, 0, SEEK_END); |
| if (current > 0) { | |
| - | if (count == 0) |
| - | continue; /* showing zero bytes is easy :) */ |
| - | current -= count; |
| + | unsigned off; |
| + | if (COUNT_BYTES) { |
| + | /* Optimizing count-bytes case if the file is seekable. |
| + | * Beware of backing up too far. |
| + | * Also we exclude files with size 0 (because of /proc/xxx) */ |
| + | if (count == 0) |
| + | continue; /* showing zero bytes is easy :) */ |
| + | current -= count; |
| + | if (current < 0) |
| + | current = 0; |
| + | xlseek(fd, current, SEEK_SET); |
| + | bb_copyfd_size(fd, STDOUT_FILENO, count); |
| + | continue; |
| + | } |
| + | #if 1 /* This is technically incorrect for *LONG* strings, but very useful */ |
| + | /* Optimizing count-lines case if the file is seekable. |
| + | * We assume the lines are <64k. |
| + | * (Users complain that tail takes too long |
| + | * on multi-gigabyte files) */ |
| + | off = (count | 0xf); /* for small counts, be more paranoid */ |
| + | if (off > (INT_MAX / (64*1024))) |
| + | off = (INT_MAX / (64*1024)); |
| + | current -= off * (64*1024); |
| if (current < 0) | |
| current = 0; | |
| - | xlseek(fds[i], current, SEEK_SET); |
| - | bb_copyfd_size(fds[i], STDOUT_FILENO, count); |
| - | continue; |
| + | xlseek(fd, current, SEEK_SET); |
| + | #endif |
| } | |
| } | |
| buf = tailbuf; | |
| taillen = 0; | |
| /* "We saw 1st line/byte". | |
| - | * Used only by +N code ("start from Nth", 1-based) */ |
| + | * Used only by +N code ("start from Nth", 1-based): */ |
| seen = 1; | |
| newlines_seen = 0; | |
| - | while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) { |
| + | while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) { |
| if (from_top) { | |
| int nwrite = nread; | |
| if (seen < count) { | |