mmap() doesn't work on files >2GB as documented in its man page. The following code is in /usr/src/usr.bin/tail/forward.c: if ((start = mmap(NULL, (size_t)size, PROT_READ, MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) { ierr(); return; } Unfortunately, after returning from the rlines function which contains that code, tail attempts to display any data that has come in "since we read the file". In this case, the file has not been read and tail spits out the entire contents of the file. Fix: Probably one of: * Detect sizes > mmap()'s limit and exit with an appropriate message. * Dump out when mmap() fails. * Use a more complicated algorithm that can handle large files. How-To-Repeat: $ tail <file-larger-than-2GB>
I've produced a patch which works by mapping 4MB chunks of the file at a time, instead of trying to map the whole file. It seems to work reasonably well, and seems to produce the same results as the original version of tail - other than on large files where it works correctly. "tail -r" also suffers from similar problems, which I could produce a patch for if people think this is the correct way to do things. David. --- forward.c.orig Mon Dec 13 09:40:31 1999 +++ forward.c Mon Dec 13 01:11:42 1999 @@ -207,9 +207,11 @@ long off; struct stat *sbp; { - register off_t size; + register off_t size, curoff; register char *p; char *start; + off_t mapoff; + size_t maplen; if (!(size = sbp->st_size)) return; @@ -220,27 +222,59 @@ return; } - if ((start = mmap(NULL, (size_t)size, - PROT_READ, MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) { - ierr(); - return; + start = NULL; + for (curoff = size - 1, mapoff = size; curoff >= 0; curoff--) { + if (curoff < mapoff) { + if (start && munmap(start, maplen)) { + ierr(); + return; + } + mapoff = curoff & (~((4<<20)-1)); + maplen = curoff - mapoff + 1; + if ((start = mmap(NULL, maplen, PROT_READ, + MAP_SHARED, fileno(fp), mapoff)) == MAP_FAILED) { + ierr(); + return; + } + } + p = start + (curoff - mapoff); + /* Last char is special, ignore whether newline or not. */ + if (*p == '\n' && curoff != size -1 && !--off) { + curoff++; + break; + } } - /* Last char is special, ignore whether newline or not. */ - for (p = start + size - 1; --size;) - if (*--p == '\n' && !--off) { - ++p; - break; + if (curoff < 0) + curoff = 0; + + while (curoff != size) { + if (curoff < mapoff || curoff >= mapoff + maplen) { + if (start && munmap(start, maplen)) { + ierr(); + return; + } + mapoff = curoff & (~((4<<20)-1)); + maplen = 4<<20; + if (mapoff + maplen > size) + maplen = size - mapoff; + if ((start = mmap(NULL, maplen, PROT_READ, + MAP_SHARED, fileno(fp), mapoff)) == MAP_FAILED) { + ierr(); + return; + } } + p = start + (curoff - mapoff); + WR(p, maplen - (curoff - mapoff)); + curoff += maplen - (curoff - mapoff); + } /* Set the file pointer to reflect the length displayed. */ - size = sbp->st_size - size; - WR(p, size); if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) { ierr(); return; } - if (munmap(start, (size_t)sbp->st_size)) { + if (start && munmap(start, maplen)) { ierr(); return; }
Responsible Changed From-To: freebsd-bugs->dwmalone Of interest to me.
> I've tested this with the patched forward.c file which i have attached and > it's still not working. It was a stupid problem - I'd fixed the problem, but left in a check that the file had to be smaller than 2GB! Try the following, it seemed to work on a 13GB file for me. David. Index: forward.c =================================================================== RCS file: /cvs/FreeBSD-CVS/src/usr.bin/tail/forward.c,v retrieving revision 1.16 diff -u -r1.16 forward.c --- forward.c 2000/12/02 19:10:12 1.16 +++ forward.c 2000/12/16 12:30:32 @@ -269,40 +269,68 @@ long off; struct stat *sbp; { - register off_t size; + off_t size, curoff; register char *p; char *start; + off_t mapoff; + size_t maplen; if (!(size = sbp->st_size)) return; - if (size > SIZE_T_MAX) { - errno = EFBIG; - ierr(); - return; + start = NULL; + for (curoff = size - 1, mapoff = size; curoff >= 0; curoff--) { + if (curoff < mapoff) { + if (start && munmap(start, maplen)) { + ierr(); + return; + } + mapoff = curoff & (~((4<<20)-1)); + maplen = curoff - mapoff + 1; + if ((start = mmap(NULL, maplen, PROT_READ, + MAP_SHARED, fileno(fp), mapoff)) == MAP_FAILED) { + ierr(); + return; + } + } + p = start + (curoff - mapoff); + /* Last char is special, ignore whether newline or not. */ + if (*p == '\n' && curoff != size -1 && !--off) { + curoff++; + break; + } } - if ((start = mmap(NULL, (size_t)size, - PROT_READ, MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) { - ierr(); - return; - } + if (curoff < 0) + curoff = 0; - /* Last char is special, ignore whether newline or not. */ - for (p = start + size - 1; --size;) - if (*--p == '\n' && !--off) { - ++p; - break; + while (curoff != size) { + if (curoff < mapoff || curoff >= mapoff + maplen) { + if (start && munmap(start, maplen)) { + ierr(); + return; + } + mapoff = curoff & (~((4<<20)-1)); + maplen = 4<<20; + if (mapoff + maplen > size) + maplen = size - mapoff; + if ((start = mmap(NULL, maplen, PROT_READ, + MAP_SHARED, fileno(fp), mapoff)) == MAP_FAILED) { + ierr(); + return; + } } + p = start + (curoff - mapoff); + WR(p, maplen - (curoff - mapoff)); + curoff += maplen - (curoff - mapoff); + } /* Set the file pointer to reflect the length displayed. */ - size = sbp->st_size - size; - WR(p, size); - if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) { + if (fseeko(fp, sbp->st_size, SEEK_SET) == -1) { ierr(); return; } - if (munmap(start, (size_t)sbp->st_size)) { + if (start != NULL && munmap(start, maplen)) { ierr(); return; }
State Changed From-To: open->closed Fixed in -current and 4.3.